2021-03-15 17:42:12

by Harshad Shirwadkar

[permalink] [raw]
Subject: Block allocator improvements

This patch series improves cr 0 and cr 1 passes of the allocator
signficantly. Currently, at cr 0 and 1, we perform linear lookups to
find the matching groups. That's very inefficient for large file
systems where there are millions of block groups. At cr 0, we only
care about the groups that have the largest free order >= the
request's order and at cr 1 we only care about groups where average
fragment size > the request size. so, this patchset introduces new
data structures that allow us to perform cr 0 lookup in constant time
and cr 1 lookup in log (number of groups) time instead of linear.

For cr 0, we add a list for each order and all the groups are enqueued
to the appropriate list based on the largest free order in its buddy
bitmap. This allows us to lookup a match at cr 0 in constant time.

For cr 1, we add a new rb tree of groups sorted by largest fragment
size. This allows us to lookup a match for cr 1 in log (num groups)
time.

These optimizations can be enabled by passing "mb_optimize_scan" mount
option.

These changes may result in allocations to be spread across the block
device. While that would not matter some block devices (such as flash)
it may be a cause of concern for other block devices that benefit from
storing related content togetther such as disk. However, it can be
argued that in high fragmentation scenrio, especially for large disks,
it's still worth optimizing the scanning since in such cases, we get
cpu bound on group scanning instead of getting IO bound. Perhaps, in
future, we could dynamically turn this new optimization on based on
fragmentation levels for such devices.

Verified that there are no regressions in smoke tests (-g quick -c 4k).

Also, to demonstrate the effectiveness for the patch series, following
experiment was performed:

Created a highly fragmented disk of size 65TB. The disk had no
contiguous 2M regions. Following command was run consecutively for 3
times:

time dd if=/dev/urandom of=file bs=2M count=10

Here are the results with and without cr 0/1 optimizations:

|---------+------------------------------+---------------------------|
| | Without CR 0/1 Optimizations | With CR 0/1 Optimizations |
|---------+------------------------------+---------------------------|
| 1st run | 5m1.871s | 2m47.642s |
| 2nd run | 2m28.390s | 0m0.611s |
| 3rd run | 2m26.530s | 0m1.255s |
|---------+------------------------------+---------------------------|

The patch [3/6] "ext4: add mballoc stats proc file" is a modified
version of the patch originally written by Artem Blagodarenko
([email protected]). With that patch, I ran following
command with and without optimizations.

dd if=/dev/zero of=/mnt/file bs=2M count=2 conv=fsync

Without optimizations:

useless_c0_loops: 3
useless_c1_loops: 39
useless_c2_loops: 0
useless_c3_loops: 0

With optimizations:

useless_c0_loops: 0
useless_c1_loops: 0
useless_c2_loops: 0
useless_c3_loops: 0

This shows that CR0 and CR1 optimizations get rid of useless CR0 and
CR1 loops altogether thereby significantly reducing the number of
groups that get considered.

Changes from V3:
----------------

- This feature is now enabled by default for disks which have at least
16 groups. This can be turned off by passing mb_optimize_scan=0
mount option and can be turned on unconditionally by passing
mb_optimize_scan=1 mount option.

- Reorganized stats by cr level

- Added ability to send parsed options back to the caller in
parse_options() functions in super.c

Signed-off-by: Harshad Shirwadkar <[email protected]>

Harshad Shirwadkar (6):
ext4: drop s_mb_bal_lock and convert protected fields to atomic
ext4: add ability to return parsed options from parse_options
ext4: add mballoc stats proc file
ext4: add MB_NUM_ORDERS macro
ext4: improve cr 0 / cr 1 group scanning
ext4: add proc files to monitor new structures

fs/ext4/ext4.h | 30 ++-
fs/ext4/mballoc.c | 567 +++++++++++++++++++++++++++++++++++++++++++---
fs/ext4/mballoc.h | 22 +-
fs/ext4/super.c | 78 +++++--
fs/ext4/sysfs.c | 6 +
5 files changed, 646 insertions(+), 57 deletions(-)

--
2.31.0.rc2.261.g7f71774620-goog


2021-03-15 17:42:12

by Harshad Shirwadkar

[permalink] [raw]
Subject: [PATCH v4 3/6] ext4: add mballoc stats proc file

Add new stats for measuring the performance of mballoc. This patch is
forked from Artem Blagodarenko's work that can be found here:

https://github.com/lustre/lustre-release/blob/master/ldiskfs/kernel_patches/patches/rhel8/ext4-simple-blockalloc.patch

This patch reorganizes the stats by cr level. This is how the output
looks like:

mballoc:
reqs: 0
success: 0
groups_scanned: 0
cr0_stats:
hits: 0
groups_considered: 0
useless_loops: 0
bad_suggestions: 0
cr1_stats:
hits: 0
groups_considered: 0
useless_loops: 0
bad_suggestions: 0
cr2_stats:
hits: 0
groups_considered: 0
useless_loops: 0
cr3_stats:
hits: 0
groups_considered: 0
useless_loops: 0
extents_scanned: 0
goal_hits: 0
2^n_hits: 0
breaks: 0
lost: 0
buddies_generated: 0/40
buddies_time_used: 0
preallocated: 0
discarded: 0

Signed-off-by: Harshad Shirwadkar <[email protected]>
Reviewed-by: Andreas Dilger <[email protected]>
---
fs/ext4/ext4.h | 5 ++++
fs/ext4/mballoc.c | 75 +++++++++++++++++++++++++++++++++++++++++++++--
fs/ext4/sysfs.c | 2 ++
3 files changed, 80 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index cb0724b87d54..85eeeba3bca3 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1549,9 +1549,13 @@ struct ext4_sb_info {
atomic_t s_bal_success; /* we found long enough chunks */
atomic_t s_bal_allocated; /* in blocks */
atomic_t s_bal_ex_scanned; /* total extents scanned */
+ atomic_t s_bal_groups_scanned; /* number of groups scanned */
atomic_t s_bal_goals; /* goal hits */
atomic_t s_bal_breaks; /* too long searches */
atomic_t s_bal_2orders; /* 2^order hits */
+ atomic64_t s_bal_cX_groups_considered[4];
+ atomic64_t s_bal_cX_hits[4];
+ atomic64_t s_bal_cX_failed[4]; /* cX loop didn't find blocks */
atomic_t s_mb_buddies_generated; /* number of buddies generated */
atomic64_t s_mb_generation_time;
atomic_t s_mb_lost_chunks;
@@ -2808,6 +2812,7 @@ int __init ext4_fc_init_dentry_cache(void);
extern const struct seq_operations ext4_mb_seq_groups_ops;
extern long ext4_mb_stats;
extern long ext4_mb_max_to_scan;
+extern int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset);
extern int ext4_mb_init(struct super_block *);
extern int ext4_mb_release(struct super_block *);
extern ext4_fsblk_t ext4_mb_new_blocks(handle_t *,
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 07b78a3cc421..a4b71c9c1e66 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2146,6 +2146,8 @@ static int ext4_mb_good_group_nolock(struct ext4_allocation_context *ac,
ext4_grpblk_t free;
int ret = 0;

+ if (sbi->s_mb_stats)
+ atomic64_inc(&sbi->s_bal_cX_groups_considered[ac->ac_criteria]);
if (should_lock)
ext4_lock_group(sb, group);
free = grp->bb_free;
@@ -2420,6 +2422,9 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
if (ac->ac_status != AC_STATUS_CONTINUE)
break;
}
+ /* Processed all groups and haven't found blocks */
+ if (sbi->s_mb_stats && i == ngroups)
+ atomic64_inc(&sbi->s_bal_cX_failed[cr]);
}

if (ac->ac_b_ex.fe_len > 0 && ac->ac_status != AC_STATUS_FOUND &&
@@ -2449,6 +2454,9 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
goto repeat;
}
}
+
+ if (sbi->s_mb_stats && ac->ac_status == AC_STATUS_FOUND)
+ atomic64_inc(&sbi->s_bal_cX_hits[ac->ac_criteria]);
out:
if (!err && ac->ac_status != AC_STATUS_FOUND && first_err)
err = first_err;
@@ -2548,6 +2556,67 @@ const struct seq_operations ext4_mb_seq_groups_ops = {
.show = ext4_mb_seq_groups_show,
};

+int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset)
+{
+ struct super_block *sb = (struct super_block *)seq->private;
+ struct ext4_sb_info *sbi = EXT4_SB(sb);
+
+ seq_puts(seq, "mballoc:\n");
+ if (!sbi->s_mb_stats) {
+ seq_puts(seq, "\tmb stats collection turned off.\n");
+ seq_puts(seq, "\tTo enable, please write \"1\" to sysfs file mb_stats.\n");
+ return 0;
+ }
+ seq_printf(seq, "\treqs: %u\n", atomic_read(&sbi->s_bal_reqs));
+ seq_printf(seq, "\tsuccess: %u\n", atomic_read(&sbi->s_bal_success));
+
+ seq_printf(seq, "\tgroups_scanned: %u\n", atomic_read(&sbi->s_bal_groups_scanned));
+
+ seq_puts(seq, "\tcr0_stats:\n");
+ seq_printf(seq, "\t\thits: %llu\n", atomic64_read(&sbi->s_bal_cX_hits[0]));
+ seq_printf(seq, "\t\tgroups_considered: %llu\n",
+ atomic64_read(&sbi->s_bal_cX_groups_considered[0]));
+ seq_printf(seq, "\t\tuseless_loops: %llu\n",
+ atomic64_read(&sbi->s_bal_cX_failed[0]));
+
+ seq_puts(seq, "\tcr1_stats:\n");
+ seq_printf(seq, "\t\thits: %llu\n", atomic64_read(&sbi->s_bal_cX_hits[1]));
+ seq_printf(seq, "\t\tgroups_considered: %llu\n",
+ atomic64_read(&sbi->s_bal_cX_groups_considered[1]));
+ seq_printf(seq, "\t\tuseless_loops: %llu\n",
+ atomic64_read(&sbi->s_bal_cX_failed[1]));
+
+ seq_puts(seq, "\tcr2_stats:\n");
+ seq_printf(seq, "\t\thits: %llu\n", atomic64_read(&sbi->s_bal_cX_hits[2]));
+ seq_printf(seq, "\t\tgroups_considered: %llu\n",
+ atomic64_read(&sbi->s_bal_cX_groups_considered[2]));
+ seq_printf(seq, "\t\tuseless_loops: %llu\n",
+ atomic64_read(&sbi->s_bal_cX_failed[2]));
+
+ seq_puts(seq, "\tcr3_stats:\n");
+ seq_printf(seq, "\t\thits: %llu\n", atomic64_read(&sbi->s_bal_cX_hits[3]));
+ seq_printf(seq, "\t\tgroups_considered: %llu\n",
+ atomic64_read(&sbi->s_bal_cX_groups_considered[3]));
+ seq_printf(seq, "\t\tuseless_loops: %llu\n",
+ atomic64_read(&sbi->s_bal_cX_failed[3]));
+ seq_printf(seq, "\textents_scanned: %u\n", atomic_read(&sbi->s_bal_ex_scanned));
+ seq_printf(seq, "\t\tgoal_hits: %u\n", atomic_read(&sbi->s_bal_goals));
+ seq_printf(seq, "\t\t2^n_hits: %u\n", atomic_read(&sbi->s_bal_2orders));
+ seq_printf(seq, "\t\tbreaks: %u\n", atomic_read(&sbi->s_bal_breaks));
+ seq_printf(seq, "\t\tlost: %u\n", atomic_read(&sbi->s_mb_lost_chunks));
+
+ seq_printf(seq, "\tbuddies_generated: %u/%u\n",
+ atomic_read(&sbi->s_mb_buddies_generated),
+ ext4_get_groups_count(sb));
+ seq_printf(seq, "\tbuddies_time_used: %llu\n",
+ atomic64_read(&sbi->s_mb_generation_time));
+ seq_printf(seq, "\tpreallocated: %u\n",
+ atomic_read(&sbi->s_mb_preallocated));
+ seq_printf(seq, "\tdiscarded: %u\n",
+ atomic_read(&sbi->s_mb_discarded));
+ return 0;
+}
+
static struct kmem_cache *get_groupinfo_cache(int blocksize_bits)
{
int cache_index = blocksize_bits - EXT4_MIN_BLOCK_LOG_SIZE;
@@ -2968,9 +3037,10 @@ int ext4_mb_release(struct super_block *sb)
atomic_read(&sbi->s_bal_reqs),
atomic_read(&sbi->s_bal_success));
ext4_msg(sb, KERN_INFO,
- "mballoc: %u extents scanned, %u goal hits, "
+ "mballoc: %u extents scanned, %u groups scanned, %u goal hits, "
"%u 2^N hits, %u breaks, %u lost",
atomic_read(&sbi->s_bal_ex_scanned),
+ atomic_read(&sbi->s_bal_groups_scanned),
atomic_read(&sbi->s_bal_goals),
atomic_read(&sbi->s_bal_2orders),
atomic_read(&sbi->s_bal_breaks),
@@ -3573,12 +3643,13 @@ static void ext4_mb_collect_stats(struct ext4_allocation_context *ac)
{
struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);

- if (sbi->s_mb_stats && ac->ac_g_ex.fe_len > 1) {
+ if (sbi->s_mb_stats && ac->ac_g_ex.fe_len >= 1) {
atomic_inc(&sbi->s_bal_reqs);
atomic_add(ac->ac_b_ex.fe_len, &sbi->s_bal_allocated);
if (ac->ac_b_ex.fe_len >= ac->ac_o_ex.fe_len)
atomic_inc(&sbi->s_bal_success);
atomic_add(ac->ac_found, &sbi->s_bal_ex_scanned);
+ atomic_add(ac->ac_groups_scanned, &sbi->s_bal_groups_scanned);
if (ac->ac_g_ex.fe_start == ac->ac_b_ex.fe_start &&
ac->ac_g_ex.fe_group == ac->ac_b_ex.fe_group)
atomic_inc(&sbi->s_bal_goals);
diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c
index 075aa3a19ff5..59ca9d73b42f 100644
--- a/fs/ext4/sysfs.c
+++ b/fs/ext4/sysfs.c
@@ -521,6 +521,8 @@ int ext4_register_sysfs(struct super_block *sb)
ext4_fc_info_show, sb);
proc_create_seq_data("mb_groups", S_IRUGO, sbi->s_proc,
&ext4_mb_seq_groups_ops, sb);
+ proc_create_single_data("mb_stats", 0444, sbi->s_proc,
+ ext4_seq_mb_stats_show, sb);
}
return 0;
}
--
2.31.0.rc2.261.g7f71774620-goog

2021-03-15 17:42:13

by Harshad Shirwadkar

[permalink] [raw]
Subject: [PATCH v4 5/6] ext4: improve cr 0 / cr 1 group scanning

Instead of traversing through groups linearly, scan groups in specific
orders at cr 0 and cr 1. At cr 0, we want to find groups that have the
largest free order >= the order of the request. So, with this patch,
we maintain lists for each possible order and insert each group into a
list based on the largest free order in its buddy bitmap. During cr 0
allocation, we traverse these lists in the increasing order of largest
free orders. This allows us to find a group with the best available cr
0 match in constant time. If nothing can be found, we fallback to cr 1
immediately.

At CR1, the story is slightly different. We want to traverse in the
order of increasing average fragment size. For CR1, we maintain a rb
tree of groupinfos which is sorted by average fragment size. Instead
of traversing linearly, at CR1, we traverse in the order of increasing
average fragment size, starting at the most optimal group. This brings
down cr 1 search complexity to log(num groups).

For cr >= 2, we just perform the linear search as before. Also, in
case of lock contention, we intermittently fallback to linear search
even in CR 0 and CR 1 cases. This allows us to proceed during the
allocation path even in case of high contention.

There is an opportunity to do optimization at CR2 too. That's because
at CR2 we only consider groups where bb_free counter (number of free
blocks) is greater than the request extent size. That's left as future
work.

All the changes introduced in this patch are protected under a new
mount option "mb_optimize_scan".

Signed-off-by: Harshad Shirwadkar <[email protected]>
Reported-by: kernel test robot <[email protected]>
Reported-by: Dan Carpenter <[email protected]>
---
fs/ext4/ext4.h | 19 ++-
fs/ext4/mballoc.c | 376 ++++++++++++++++++++++++++++++++++++++++++++--
fs/ext4/mballoc.h | 17 ++-
fs/ext4/super.c | 28 +++-
fs/ext4/sysfs.c | 2 +
5 files changed, 427 insertions(+), 15 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 85eeeba3bca3..5930c8cb5159 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -162,7 +162,10 @@ enum SHIFT_DIRECTION {
#define EXT4_MB_USE_RESERVED 0x2000
/* Do strict check for free blocks while retrying block allocation */
#define EXT4_MB_STRICT_CHECK 0x4000
-
+/* Large fragment size list lookup succeeded at least once for cr = 0 */
+#define EXT4_MB_CR0_OPTIMIZED 0x8000
+/* Avg fragment size rb tree lookup succeeded at least once for cr = 1 */
+#define EXT4_MB_CR1_OPTIMIZED 0x00010000
struct ext4_allocation_request {
/* target inode for block we're allocating */
struct inode *inode;
@@ -1247,7 +1250,9 @@ struct ext4_inode_info {
#define EXT4_MOUNT2_JOURNAL_FAST_COMMIT 0x00000010 /* Journal fast commit */
#define EXT4_MOUNT2_DAX_NEVER 0x00000020 /* Do not allow Direct Access */
#define EXT4_MOUNT2_DAX_INODE 0x00000040 /* For printing options only */
-
+#define EXT4_MOUNT2_MB_OPTIMIZE_SCAN 0x00000080 /* Optimize group
+ * scanning in mballoc
+ */

#define clear_opt(sb, opt) EXT4_SB(sb)->s_mount_opt &= \
~EXT4_MOUNT_##opt
@@ -1527,9 +1532,14 @@ struct ext4_sb_info {
unsigned int s_mb_free_pending;
struct list_head s_freed_data_list; /* List of blocks to be freed
after commit completed */
+ struct rb_root s_mb_avg_fragment_size_root;
+ rwlock_t s_mb_rb_lock;
+ struct list_head *s_mb_largest_free_orders;
+ rwlock_t *s_mb_largest_free_orders_locks;

/* tunables */
unsigned long s_stripe;
+ unsigned int s_mb_linear_limit;
unsigned int s_mb_stream_request;
unsigned int s_mb_max_to_scan;
unsigned int s_mb_min_to_scan;
@@ -1553,6 +1563,8 @@ struct ext4_sb_info {
atomic_t s_bal_goals; /* goal hits */
atomic_t s_bal_breaks; /* too long searches */
atomic_t s_bal_2orders; /* 2^order hits */
+ atomic_t s_bal_cr0_bad_suggestions;
+ atomic_t s_bal_cr1_bad_suggestions;
atomic64_t s_bal_cX_groups_considered[4];
atomic64_t s_bal_cX_hits[4];
atomic64_t s_bal_cX_failed[4]; /* cX loop didn't find blocks */
@@ -3309,11 +3321,14 @@ struct ext4_group_info {
ext4_grpblk_t bb_free; /* total free blocks */
ext4_grpblk_t bb_fragments; /* nr of freespace fragments */
ext4_grpblk_t bb_largest_free_order;/* order of largest frag in BG */
+ ext4_group_t bb_group; /* Group number */
struct list_head bb_prealloc_list;
#ifdef DOUBLE_CHECK
void *bb_bitmap;
#endif
struct rw_semaphore alloc_sem;
+ struct rb_node bb_avg_fragment_size_rb;
+ struct list_head bb_largest_free_order_node;
ext4_grpblk_t bb_counters[]; /* Nr of free power-of-two-block
* regions, index is order.
* bb_counters[3] = 5 means
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 15127d815461..fb53ec1e1d37 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -127,11 +127,50 @@
* smallest multiple of the stripe value (sbi->s_stripe) which is
* greater than the default mb_group_prealloc.
*
+ * If "mb_optimize_scan" mount option is set, we maintain in memory group info
+ * structures in two data structures:
+ *
+ * 1) Array of largest free order lists (sbi->s_mb_largest_free_orders)
+ *
+ * Locking: sbi->s_mb_largest_free_orders_locks(array of rw locks)
+ *
+ * This is an array of lists where the index in the array represents the
+ * largest free order in the buddy bitmap of the participating group infos of
+ * that list. So, there are exactly MB_NUM_ORDERS(sb) (which means total
+ * number of buddy bitmap orders possible) number of lists. Group-infos are
+ * placed in appropriate lists.
+ *
+ * 2) Average fragment size rb tree (sbi->s_mb_avg_fragment_size_root)
+ *
+ * Locking: sbi->s_mb_rb_lock (rwlock)
+ *
+ * This is a red black tree consisting of group infos and the tree is sorted
+ * by average fragment sizes (which is calculated as ext4_group_info->bb_free
+ * / ext4_group_info->bb_fragments).
+ *
+ * When "mb_optimize_scan" mount option is set, mballoc consults the above data
+ * structures to decide the order in which groups are to be traversed for
+ * fulfilling an allocation request.
+ *
+ * At CR = 0, we look for groups which have the largest_free_order >= the order
+ * of the request. We directly look at the largest free order list in the data
+ * structure (1) above where largest_free_order = order of the request. If that
+ * list is empty, we look at remaining list in the increasing order of
+ * largest_free_order. This allows us to perform CR = 0 lookup in O(1) time.
+ *
+ * At CR = 1, we only consider groups where average fragment size > request
+ * size. So, we lookup a group which has average fragment size just above or
+ * equal to request size using our rb tree (data structure 2) in O(log N) time.
+ *
+ * If "mb_optimize_scan" mount option is not set, mballoc traverses groups in
+ * linear order which requires O(N) search time for each CR 0 and CR 1 phase.
+ *
* The regular allocator (using the buddy cache) supports a few tunables.
*
* /sys/fs/ext4/<partition>/mb_min_to_scan
* /sys/fs/ext4/<partition>/mb_max_to_scan
* /sys/fs/ext4/<partition>/mb_order2_req
+ * /sys/fs/ext4/<partition>/mb_linear_limit
*
* The regular allocator uses buddy scan only if the request len is power of
* 2 blocks and the order of allocation is >= sbi->s_mb_order2_reqs. The
@@ -149,6 +188,16 @@
* can be used for allocation. ext4_mb_good_group explains how the groups are
* checked.
*
+ * When "mb_optimize_scan" is turned on, as mentioned above, the groups may not
+ * get traversed linearly. That may result in subsequent allocations being not
+ * close to each other. And so, the underlying device may get filled up in a
+ * non-linear fashion. While that may not matter on non-rotational devices, for
+ * rotational devices that may result in higher seek times. "mb_linear_limit"
+ * tells mballoc how many groups mballoc should search linearly before
+ * performing consulting above data structures for more efficient lookups. For
+ * non rotational devices, this value defaults to 0 and for rotational devices
+ * this is set to MB_DEFAULT_LINEAR_LIMIT.
+ *
* Both the prealloc space are getting populated as above. So for the first
* request we will hit the buddy cache which will result in this prealloc
* space getting filled. The prealloc space is then later used for the
@@ -299,6 +348,8 @@
* - bitlock on a group (group)
* - object (inode/locality) (object)
* - per-pa lock (pa)
+ * - cr0 lists lock (cr0)
+ * - cr1 tree lock (cr1)
*
* Paths:
* - new pa
@@ -328,6 +379,9 @@
* group
* object
*
+ * - allocation path (ext4_mb_regular_allocator)
+ * group
+ * cr0/cr1
*/
static struct kmem_cache *ext4_pspace_cachep;
static struct kmem_cache *ext4_ac_cachep;
@@ -351,6 +405,9 @@ static void ext4_mb_generate_from_freelist(struct super_block *sb, void *bitmap,
ext4_group_t group);
static void ext4_mb_new_preallocation(struct ext4_allocation_context *ac);

+static bool ext4_mb_good_group(struct ext4_allocation_context *ac,
+ ext4_group_t group, int cr);
+
/*
* The algorithm using this percpu seq counter goes below:
* 1. We sample the percpu discard_pa_seq counter before trying for block
@@ -744,6 +801,251 @@ static void ext4_mb_mark_free_simple(struct super_block *sb,
}
}

+static void ext4_mb_rb_insert(struct rb_root *root, struct rb_node *new,
+ int (*cmp)(struct rb_node *, struct rb_node *))
+{
+ struct rb_node **iter = &root->rb_node, *parent = NULL;
+
+ while (*iter) {
+ parent = *iter;
+ if (cmp(new, *iter))
+ iter = &((*iter)->rb_left);
+ else
+ iter = &((*iter)->rb_right);
+ }
+
+ rb_link_node(new, parent, iter);
+ rb_insert_color(new, root);
+}
+
+static int
+ext4_mb_avg_fragment_size_cmp(struct rb_node *rb1, struct rb_node *rb2)
+{
+ struct ext4_group_info *grp1 = rb_entry(rb1,
+ struct ext4_group_info,
+ bb_avg_fragment_size_rb);
+ struct ext4_group_info *grp2 = rb_entry(rb2,
+ struct ext4_group_info,
+ bb_avg_fragment_size_rb);
+ int num_frags_1, num_frags_2;
+
+ num_frags_1 = grp1->bb_fragments ?
+ grp1->bb_free / grp1->bb_fragments : 0;
+ num_frags_2 = grp2->bb_fragments ?
+ grp2->bb_free / grp2->bb_fragments : 0;
+
+ return (num_frags_1 < num_frags_2);
+}
+
+/*
+ * Reinsert grpinfo into the avg_fragment_size tree with new average
+ * fragment size.
+ */
+static void
+mb_update_avg_fragment_size(struct super_block *sb, struct ext4_group_info *grp)
+{
+ struct ext4_sb_info *sbi = EXT4_SB(sb);
+
+ if (!test_opt2(sb, MB_OPTIMIZE_SCAN) || grp->bb_free == 0)
+ return;
+
+ write_lock(&sbi->s_mb_rb_lock);
+ if (!RB_EMPTY_NODE(&grp->bb_avg_fragment_size_rb)) {
+ rb_erase(&grp->bb_avg_fragment_size_rb,
+ &sbi->s_mb_avg_fragment_size_root);
+ RB_CLEAR_NODE(&grp->bb_avg_fragment_size_rb);
+ }
+
+ ext4_mb_rb_insert(&sbi->s_mb_avg_fragment_size_root,
+ &grp->bb_avg_fragment_size_rb,
+ ext4_mb_avg_fragment_size_cmp);
+ write_unlock(&sbi->s_mb_rb_lock);
+}
+
+/*
+ * Choose next group by traversing largest_free_order lists. Return 0 if next
+ * group was selected optimally. Return 1 if next group was not selected
+ * optimally. Updates *new_cr if cr level needs an update.
+ */
+static int ext4_mb_choose_next_group_cr0(struct ext4_allocation_context *ac,
+ int *new_cr, ext4_group_t *group, ext4_group_t ngroups)
+{
+ struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
+ struct ext4_group_info *iter, *grp;
+ int i;
+
+ if (ac->ac_status == AC_STATUS_FOUND)
+ return 1;
+
+ if (unlikely(sbi->s_mb_stats && ac->ac_flags & EXT4_MB_CR0_OPTIMIZED))
+ atomic_inc(&sbi->s_bal_cr0_bad_suggestions);
+
+ grp = NULL;
+ for (i = ac->ac_2order; i < MB_NUM_ORDERS(ac->ac_sb); i++) {
+ if (list_empty(&sbi->s_mb_largest_free_orders[i]))
+ continue;
+ read_lock(&sbi->s_mb_largest_free_orders_locks[i]);
+ if (list_empty(&sbi->s_mb_largest_free_orders[i])) {
+ read_unlock(&sbi->s_mb_largest_free_orders_locks[i]);
+ continue;
+ }
+ grp = NULL;
+ list_for_each_entry(iter, &sbi->s_mb_largest_free_orders[i],
+ bb_largest_free_order_node) {
+ if (sbi->s_mb_stats)
+ atomic64_inc(&sbi->s_bal_cX_groups_considered[0]);
+ if (likely(ext4_mb_good_group(ac, iter->bb_group, 0))) {
+ grp = iter;
+ break;
+ }
+ }
+ read_unlock(&sbi->s_mb_largest_free_orders_locks[i]);
+ if (grp)
+ break;
+ }
+
+ if (!grp) {
+ /* Increment cr and search again */
+ *new_cr = 1;
+ } else {
+ *group = grp->bb_group;
+ ac->ac_last_optimal_group = *group;
+ ac->ac_flags |= EXT4_MB_CR0_OPTIMIZED;
+ }
+ return 0;
+}
+
+/*
+ * Choose next group by traversing average fragment size tree. Return 0 if next
+ * group was selected optimally. Return 1 if next group could not selected
+ * optimally (due to lock contention). Updates *new_cr if cr lvel needs an
+ * update.
+ */
+static int ext4_mb_choose_next_group_cr1(struct ext4_allocation_context *ac,
+ int *new_cr, ext4_group_t *group, ext4_group_t ngroups)
+{
+ struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
+ int avg_fragment_size, best_so_far;
+ struct rb_node *node, *found;
+ struct ext4_group_info *grp;
+
+ /*
+ * If there is contention on the lock, instead of waiting for the lock
+ * to become available, just continue searching lineraly. We'll resume
+ * our rb tree search later starting at ac->ac_last_optimal_group.
+ */
+ if (!read_trylock(&sbi->s_mb_rb_lock))
+ return 1;
+
+ if (unlikely(ac->ac_flags & EXT4_MB_CR1_OPTIMIZED)) {
+ if (sbi->s_mb_stats)
+ atomic_inc(&sbi->s_bal_cr1_bad_suggestions);
+ /* We have found something at CR 1 in the past */
+ grp = ext4_get_group_info(ac->ac_sb, ac->ac_last_optimal_group);
+ for (found = rb_next(&grp->bb_avg_fragment_size_rb); found != NULL;
+ found = rb_next(found)) {
+ grp = rb_entry(found, struct ext4_group_info,
+ bb_avg_fragment_size_rb);
+ if (sbi->s_mb_stats)
+ atomic64_inc(&sbi->s_bal_cX_groups_considered[1]);
+ if (likely(ext4_mb_good_group(ac, grp->bb_group, 1)))
+ break;
+ }
+
+ goto done;
+ }
+
+ node = sbi->s_mb_avg_fragment_size_root.rb_node;
+ best_so_far = 0;
+ found = NULL;
+
+ while (node) {
+ grp = rb_entry(node, struct ext4_group_info,
+ bb_avg_fragment_size_rb);
+ avg_fragment_size = 0;
+ /*
+ * Perform this check without locking, we'll lock later to confirm.
+ */
+ if (ext4_mb_good_group(ac, grp->bb_group, 1)) {
+ avg_fragment_size = grp->bb_fragments ?
+ grp->bb_free / grp->bb_fragments : 0;
+ if (!best_so_far || avg_fragment_size < best_so_far) {
+ best_so_far = avg_fragment_size;
+ found = node;
+ }
+ }
+ if (avg_fragment_size > ac->ac_g_ex.fe_len)
+ node = node->rb_right;
+ else
+ node = node->rb_left;
+ }
+
+done:
+ if (found) {
+ grp = rb_entry(found, struct ext4_group_info,
+ bb_avg_fragment_size_rb);
+ *group = grp->bb_group;
+ ac->ac_flags |= EXT4_MB_CR1_OPTIMIZED;
+ } else {
+ *new_cr = 2;
+ }
+
+ read_unlock(&sbi->s_mb_rb_lock);
+ ac->ac_last_optimal_group = *group;
+ return 0;
+}
+
+/*
+ * ext4_mb_choose_next_group: choose next group for allocation.
+ *
+ * @ac Allocation Context
+ * @new_cr This is an output parameter. If the there is no good group
+ * available at current CR level, this field is updated to indicate
+ * the new cr level that should be used.
+ * @group This is an input / output parameter. As an input it indicates the
+ * last group used for allocation. As output, this field indicates
+ * the next group that should be used.
+ * @ngroups Total number of groups
+ */
+static void ext4_mb_choose_next_group(struct ext4_allocation_context *ac,
+ int *new_cr, ext4_group_t *group, ext4_group_t ngroups)
+{
+ int ret;
+
+ *new_cr = ac->ac_criteria;
+
+ if (!test_opt2(ac->ac_sb, MB_OPTIMIZE_SCAN) ||
+ *new_cr >= 2 ||
+ !ext4_test_inode_flag(ac->ac_inode, EXT4_INODE_EXTENTS))
+ goto inc_and_return;
+
+ if (ac->ac_groups_linear_remaining) {
+ ac->ac_groups_linear_remaining--;
+ goto inc_and_return;
+ }
+
+ if (*new_cr == 0) {
+ ret = ext4_mb_choose_next_group_cr0(ac, new_cr, group, ngroups);
+ if (ret)
+ goto inc_and_return;
+ }
+ if (*new_cr == 1) {
+ ret = ext4_mb_choose_next_group_cr1(ac, new_cr, group, ngroups);
+ if (ret)
+ goto inc_and_return;
+ }
+ return;
+
+inc_and_return:
+ /*
+ * Artificially restricted ngroups for non-extent
+ * files makes group > ngroups possible on first loop.
+ */
+ *group = *group + 1;
+ if (*group >= ngroups)
+ *group = 0;
+}
+
/*
* Cache the order of the largest free extent we have available in this block
* group.
@@ -751,18 +1053,33 @@ static void ext4_mb_mark_free_simple(struct super_block *sb,
static void
mb_set_largest_free_order(struct super_block *sb, struct ext4_group_info *grp)
{
+ struct ext4_sb_info *sbi = EXT4_SB(sb);
int i;
- int bits;

+ if (test_opt2(sb, MB_OPTIMIZE_SCAN) && grp->bb_largest_free_order >= 0) {
+ write_lock(&sbi->s_mb_largest_free_orders_locks[
+ grp->bb_largest_free_order]);
+ list_del_init(&grp->bb_largest_free_order_node);
+ write_unlock(&sbi->s_mb_largest_free_orders_locks[
+ grp->bb_largest_free_order]);
+ }
grp->bb_largest_free_order = -1; /* uninit */

- bits = MB_NUM_ORDERS(sb) - 1;
- for (i = bits; i >= 0; i--) {
+ for (i = MB_NUM_ORDERS(sb) - 1; i >= 0; i--) {
if (grp->bb_counters[i] > 0) {
grp->bb_largest_free_order = i;
break;
}
}
+ if (test_opt2(sb, MB_OPTIMIZE_SCAN) &&
+ grp->bb_largest_free_order >= 0 && grp->bb_free) {
+ write_lock(&sbi->s_mb_largest_free_orders_locks[
+ grp->bb_largest_free_order]);
+ list_add_tail(&grp->bb_largest_free_order_node,
+ &sbi->s_mb_largest_free_orders[grp->bb_largest_free_order]);
+ write_unlock(&sbi->s_mb_largest_free_orders_locks[
+ grp->bb_largest_free_order]);
+ }
}

static noinline_for_stack
@@ -818,6 +1135,7 @@ void ext4_mb_generate_buddy(struct super_block *sb,
period = get_cycles() - period;
atomic_inc(&sbi->s_mb_buddies_generated);
atomic64_add(period, &sbi->s_mb_generation_time);
+ mb_update_avg_fragment_size(sb, grp);
}

/* The buddy information is attached the buddy cache inode
@@ -1517,6 +1835,7 @@ static void mb_free_blocks(struct inode *inode, struct ext4_buddy *e4b,

done:
mb_set_largest_free_order(sb, e4b->bd_info);
+ mb_update_avg_fragment_size(sb, e4b->bd_info);
mb_check_buddy(e4b);
}

@@ -1653,6 +1972,7 @@ static int mb_mark_used(struct ext4_buddy *e4b, struct ext4_free_extent *ex)
}
mb_set_largest_free_order(e4b->bd_sb, e4b->bd_info);

+ mb_update_avg_fragment_size(e4b->bd_sb, e4b->bd_info);
ext4_set_bits(e4b->bd_bitmap, ex->fe_start, len0);
mb_check_buddy(e4b);

@@ -2347,17 +2667,21 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
* from the goal value specified
*/
group = ac->ac_g_ex.fe_group;
+ ac->ac_last_optimal_group = group;
+ ac->ac_groups_linear_remaining = sbi->s_mb_linear_limit;
prefetch_grp = group;

- for (i = 0; i < ngroups; group++, i++) {
- int ret = 0;
+ for (i = 0; i < ngroups; i++) {
+ int ret = 0, new_cr;
+
cond_resched();
- /*
- * Artificially restricted ngroups for non-extent
- * files makes group > ngroups possible on first loop.
- */
- if (group >= ngroups)
- group = 0;
+
+ ext4_mb_choose_next_group(ac, &new_cr, &group, ngroups);
+
+ if (new_cr != cr) {
+ cr = new_cr;
+ goto repeat;
+ }

/*
* Batch reads of the block allocation bitmaps
@@ -2578,6 +2902,8 @@ int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset)
atomic64_read(&sbi->s_bal_cX_groups_considered[0]));
seq_printf(seq, "\t\tuseless_loops: %llu\n",
atomic64_read(&sbi->s_bal_cX_failed[0]));
+ seq_printf(seq, "\t\tbad_suggestions: %u\n",
+ atomic_read(&sbi->s_bal_cr0_bad_suggestions));

seq_puts(seq, "\tcr1_stats:\n");
seq_printf(seq, "\t\thits: %llu\n", atomic64_read(&sbi->s_bal_cX_hits[1]));
@@ -2585,6 +2911,8 @@ int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset)
atomic64_read(&sbi->s_bal_cX_groups_considered[1]));
seq_printf(seq, "\t\tuseless_loops: %llu\n",
atomic64_read(&sbi->s_bal_cX_failed[1]));
+ seq_printf(seq, "\t\tbad_suggestions: %u\n",
+ atomic_read(&sbi->s_bal_cr1_bad_suggestions));

seq_puts(seq, "\tcr2_stats:\n");
seq_printf(seq, "\t\thits: %llu\n", atomic64_read(&sbi->s_bal_cX_hits[2]));
@@ -2719,7 +3047,10 @@ int ext4_mb_add_groupinfo(struct super_block *sb, ext4_group_t group,
INIT_LIST_HEAD(&meta_group_info[i]->bb_prealloc_list);
init_rwsem(&meta_group_info[i]->alloc_sem);
meta_group_info[i]->bb_free_root = RB_ROOT;
+ INIT_LIST_HEAD(&meta_group_info[i]->bb_largest_free_order_node);
+ RB_CLEAR_NODE(&meta_group_info[i]->bb_avg_fragment_size_rb);
meta_group_info[i]->bb_largest_free_order = -1; /* uninit */
+ meta_group_info[i]->bb_group = group;

mb_group_bb_bitmap_alloc(sb, meta_group_info[i], group);
return 0;
@@ -2909,6 +3240,22 @@ int ext4_mb_init(struct super_block *sb)
i++;
} while (i < MB_NUM_ORDERS(sb));

+ sbi->s_mb_avg_fragment_size_root = RB_ROOT;
+ sbi->s_mb_largest_free_orders =
+ kmalloc_array(MB_NUM_ORDERS(sb), sizeof(struct list_head),
+ GFP_KERNEL);
+ if (!sbi->s_mb_largest_free_orders)
+ goto out;
+ sbi->s_mb_largest_free_orders_locks =
+ kmalloc_array(MB_NUM_ORDERS(sb), sizeof(rwlock_t),
+ GFP_KERNEL);
+ if (!sbi->s_mb_largest_free_orders_locks)
+ goto out;
+ for (i = 0; i < MB_NUM_ORDERS(sb); i++) {
+ INIT_LIST_HEAD(&sbi->s_mb_largest_free_orders[i]);
+ rwlock_init(&sbi->s_mb_largest_free_orders_locks[i]);
+ }
+ rwlock_init(&sbi->s_mb_rb_lock);

spin_lock_init(&sbi->s_md_lock);
sbi->s_mb_free_pending = 0;
@@ -2961,6 +3308,10 @@ int ext4_mb_init(struct super_block *sb)
spin_lock_init(&lg->lg_prealloc_lock);
}

+ if (blk_queue_nonrot(bdev_get_queue(sb->s_bdev)))
+ sbi->s_mb_linear_limit = 0;
+ else
+ sbi->s_mb_linear_limit = MB_DEFAULT_LINEAR_LIMIT;
/* init file for buddy data */
ret = ext4_mb_init_backend(sb);
if (ret != 0)
@@ -2972,6 +3323,8 @@ int ext4_mb_init(struct super_block *sb)
free_percpu(sbi->s_locality_groups);
sbi->s_locality_groups = NULL;
out:
+ kfree(sbi->s_mb_largest_free_orders);
+ kfree(sbi->s_mb_largest_free_orders_locks);
kfree(sbi->s_mb_offsets);
sbi->s_mb_offsets = NULL;
kfree(sbi->s_mb_maxs);
@@ -3028,6 +3381,7 @@ int ext4_mb_release(struct super_block *sb)
kvfree(group_info);
rcu_read_unlock();
}
+ kfree(sbi->s_mb_largest_free_orders);
kfree(sbi->s_mb_offsets);
kfree(sbi->s_mb_maxs);
iput(sbi->s_buddy_cache);
diff --git a/fs/ext4/mballoc.h b/fs/ext4/mballoc.h
index 68111a10cfee..02585e3cbcad 100644
--- a/fs/ext4/mballoc.h
+++ b/fs/ext4/mballoc.h
@@ -78,6 +78,18 @@
*/
#define MB_DEFAULT_MAX_INODE_PREALLOC 512

+/*
+ * Number of groups to search linearly before performing group scanning
+ * optimization.
+ */
+#define MB_DEFAULT_LINEAR_LIMIT 4
+
+/*
+ * Minimum number of groups that should be present in the file system to perform
+ * group scanning optimizations.
+ */
+#define MB_DEFAULT_LINEAR_SCAN_THRESHOLD 16
+
/*
* Number of valid buddy orders
*/
@@ -166,11 +178,14 @@ struct ext4_allocation_context {
/* copy of the best found extent taken before preallocation efforts */
struct ext4_free_extent ac_f_ex;

+ ext4_group_t ac_last_optimal_group;
+ __u32 ac_groups_considered;
+ __u32 ac_flags; /* allocation hints */
__u16 ac_groups_scanned;
+ __u16 ac_groups_linear_remaining;
__u16 ac_found;
__u16 ac_tail;
__u16 ac_buddy;
- __u16 ac_flags; /* allocation hints */
__u8 ac_status;
__u8 ac_criteria;
__u8 ac_2order; /* if request is to allocate 2^N blocks and
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 0491e7a6b04c..5b973f037298 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1687,7 +1687,7 @@ enum {
Opt_dioread_nolock, Opt_dioread_lock,
Opt_discard, Opt_nodiscard, Opt_init_itable, Opt_noinit_itable,
Opt_max_dir_size_kb, Opt_nojournal_checksum, Opt_nombcache,
- Opt_prefetch_block_bitmaps,
+ Opt_prefetch_block_bitmaps, Opt_mb_optimize_scan,
#ifdef CONFIG_EXT4_DEBUG
Opt_fc_debug_max_replay, Opt_fc_debug_force
#endif
@@ -1788,6 +1788,7 @@ static const match_table_t tokens = {
{Opt_nombcache, "nombcache"},
{Opt_nombcache, "no_mbcache"}, /* for backward compatibility */
{Opt_prefetch_block_bitmaps, "prefetch_block_bitmaps"},
+ {Opt_mb_optimize_scan, "mb_optimize_scan=%d"},
{Opt_removed, "check=none"}, /* mount option from ext2/3 */
{Opt_removed, "nocheck"}, /* mount option from ext2/3 */
{Opt_removed, "reservation"}, /* mount option from ext2/3 */
@@ -1820,6 +1821,8 @@ static ext4_fsblk_t get_sb_block(void **data)
}

#define DEFAULT_JOURNAL_IOPRIO (IOPRIO_PRIO_VALUE(IOPRIO_CLASS_BE, 3))
+#define DEFAULT_MB_OPTIMIZE_SCAN (-1)
+
static const char deprecated_msg[] =
"Mount option \"%s\" will be removed by %s\n"
"Contact [email protected] if you think we should keep it.\n";
@@ -2008,6 +2011,7 @@ static const struct mount_opts {
{Opt_nombcache, EXT4_MOUNT_NO_MBCACHE, MOPT_SET},
{Opt_prefetch_block_bitmaps, EXT4_MOUNT_PREFETCH_BLOCK_BITMAPS,
MOPT_SET},
+ {Opt_mb_optimize_scan, EXT4_MOUNT2_MB_OPTIMIZE_SCAN, MOPT_GTE0},
#ifdef CONFIG_EXT4_DEBUG
{Opt_fc_debug_force, EXT4_MOUNT2_JOURNAL_FAST_COMMIT,
MOPT_SET | MOPT_2 | MOPT_EXT4_ONLY},
@@ -2092,6 +2096,7 @@ static int ext4_set_test_dummy_encryption(struct super_block *sb,
struct ext4_parsed_options {
unsigned long journal_devnum;
unsigned int journal_ioprio;
+ int mb_optimize_scan;
};

static int handle_mount_opt(struct super_block *sb, char *opt, int token,
@@ -2388,6 +2393,13 @@ static int handle_mount_opt(struct super_block *sb, char *opt, int token,
sbi->s_mount_opt |= m->mount_opt;
} else if (token == Opt_data_err_ignore) {
sbi->s_mount_opt &= ~m->mount_opt;
+ } else if (token == Opt_mb_optimize_scan) {
+ if (arg != 0 && arg != 1) {
+ ext4_msg(sb, KERN_WARNING,
+ "mb_optimize_scan should be set to 0 or 1.");
+ return -1;
+ }
+ parsed_opts->mb_optimize_scan = arg;
} else {
if (!args->from)
arg = 1;
@@ -4034,6 +4046,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
/* Set defaults for the variables that will be set during parsing */
parsed_opts.journal_ioprio = DEFAULT_JOURNAL_IOPRIO;
parsed_opts.journal_devnum = 0;
+ parsed_opts.mb_optimize_scan = DEFAULT_MB_OPTIMIZE_SCAN;

if ((data && !orig_data) || !sbi)
goto out_free_base;
@@ -4984,6 +4997,19 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
ext4_fc_replay_cleanup(sb);

ext4_ext_init(sb);
+
+ /*
+ * Enable optimize_scan if number of groups is > threshold. This can be
+ * turned off by passing "mb_optimize_scan=0". This can also be
+ * turned on forcefully by passing "mb_optimize_scan=1".
+ */
+ if (parsed_opts.mb_optimize_scan == 1)
+ set_opt2(sb, MB_OPTIMIZE_SCAN);
+ else if (parsed_opts.mb_optimize_scan == 0)
+ clear_opt2(sb, MB_OPTIMIZE_SCAN);
+ else if (sbi->s_groups_count >= MB_DEFAULT_LINEAR_SCAN_THRESHOLD)
+ set_opt2(sb, MB_OPTIMIZE_SCAN);
+
err = ext4_mb_init(sb);
if (err) {
ext4_msg(sb, KERN_ERR, "failed to initialize mballoc (%d)",
diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c
index 59ca9d73b42f..16b8a838f631 100644
--- a/fs/ext4/sysfs.c
+++ b/fs/ext4/sysfs.c
@@ -213,6 +213,7 @@ EXT4_RW_ATTR_SBI_UI(mb_order2_req, s_mb_order2_reqs);
EXT4_RW_ATTR_SBI_UI(mb_stream_req, s_mb_stream_request);
EXT4_RW_ATTR_SBI_UI(mb_group_prealloc, s_mb_group_prealloc);
EXT4_RW_ATTR_SBI_UI(mb_max_inode_prealloc, s_mb_max_inode_prealloc);
+EXT4_RW_ATTR_SBI_UI(mb_linear_limit, s_mb_linear_limit);
EXT4_RW_ATTR_SBI_UI(extent_max_zeroout_kb, s_extent_max_zeroout_kb);
EXT4_ATTR(trigger_fs_error, 0200, trigger_test_error);
EXT4_RW_ATTR_SBI_UI(err_ratelimit_interval_ms, s_err_ratelimit_state.interval);
@@ -260,6 +261,7 @@ static struct attribute *ext4_attrs[] = {
ATTR_LIST(mb_stream_req),
ATTR_LIST(mb_group_prealloc),
ATTR_LIST(mb_max_inode_prealloc),
+ ATTR_LIST(mb_linear_limit),
ATTR_LIST(max_writeback_mb_bump),
ATTR_LIST(extent_max_zeroout_kb),
ATTR_LIST(trigger_fs_error),
--
2.31.0.rc2.261.g7f71774620-goog

2021-03-15 21:36:06

by Andreas Dilger

[permalink] [raw]
Subject: Re: Block allocator improvements

On Mar 15, 2021, at 11:37 AM, Harshad Shirwadkar <[email protected]> wrote:
>
> Created a highly fragmented disk of size 65TB. The disk had no
> contiguous 2M regions. Following command was run consecutively for 3
> times:
>
> time dd if=/dev/urandom of=file bs=2M count=10
>
> Here are the results with and without cr 0/1 optimizations:
>
> |---------+------------------------------+---------------------------|
> | | Without CR 0/1 Optimizations | With CR 0/1 Optimizations |
> |---------+------------------------------+---------------------------|
> | 1st run | 5m1.871s | 2m47.642s |
> | 2nd run | 2m28.390s | 0m0.611s |
> | 3rd run | 2m26.530s | 0m1.255s |
> |---------+------------------------------+---------------------------|

IMHO, it would be useful to include this into the 5/6 patch commit
message, so that it is available with the patch in the future.
That will show the workload and basic test environment used to
justify this change, in case there are problems/changes in the future.

Cheers, Andreas






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2021-03-15 21:54:13

by Andreas Dilger

[permalink] [raw]
Subject: Re: [PATCH v4 5/6] ext4: improve cr 0 / cr 1 group scanning

On Mar 15, 2021, at 11:37 AM, Harshad Shirwadkar <[email protected]> wrote:
>
> Instead of traversing through groups linearly, scan groups in specific
> orders at cr 0 and cr 1. At cr 0, we want to find groups that have the
> largest free order >= the order of the request. So, with this patch,
> we maintain lists for each possible order and insert each group into a
> list based on the largest free order in its buddy bitmap. During cr 0
> allocation, we traverse these lists in the increasing order of largest
> free orders. This allows us to find a group with the best available cr
> 0 match in constant time. If nothing can be found, we fallback to cr 1
> immediately.
>
> At CR1, the story is slightly different. We want to traverse in the
> order of increasing average fragment size. For CR1, we maintain a rb
> tree of groupinfos which is sorted by average fragment size. Instead
> of traversing linearly, at CR1, we traverse in the order of increasing
> average fragment size, starting at the most optimal group. This brings
> down cr 1 search complexity to log(num groups).
>
> For cr >= 2, we just perform the linear search as before. Also, in
> case of lock contention, we intermittently fallback to linear search
> even in CR 0 and CR 1 cases. This allows us to proceed during the
> allocation path even in case of high contention.
>
> There is an opportunity to do optimization at CR2 too. That's because
> at CR2 we only consider groups where bb_free counter (number of free
> blocks) is greater than the request extent size. That's left as future
> work.
>
> All the changes introduced in this patch are protected under a new
> mount option "mb_optimize_scan".
>
> Signed-off-by: Harshad Shirwadkar <[email protected]>
> Reported-by: kernel test robot <[email protected]>
> Reported-by: Dan Carpenter <[email protected]>

Reviewed-by: Andreas Dilger <[email protected]>

Cheers, Andreas






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2021-03-16 09:26:00

by Dan Carpenter

[permalink] [raw]
Subject: Re: [PATCH v4 5/6] ext4: improve cr 0 / cr 1 group scanning

On Mon, Mar 15, 2021 at 10:37:15AM -0700, Harshad Shirwadkar wrote:
> @@ -744,6 +801,251 @@ static void ext4_mb_mark_free_simple(struct super_block *sb,
> }
> }
>
> +static void ext4_mb_rb_insert(struct rb_root *root, struct rb_node *new,
> + int (*cmp)(struct rb_node *, struct rb_node *))
> +{
> + struct rb_node **iter = &root->rb_node, *parent = NULL;
> +
> + while (*iter) {
> + parent = *iter;
> + if (cmp(new, *iter))
> + iter = &((*iter)->rb_left);
> + else
> + iter = &((*iter)->rb_right);
> + }

This would be neater like so:

while (*iter) {
node = *iter;
if (cmp(new, node))
iter = &node->rb_left;
else
iter = &node->rb_right;
}

It's unexpected that the cmp() function returns bool instead of -1, 0
1 like other cmp() functions.

> +
> + rb_link_node(new, parent, iter);
> + rb_insert_color(new, root);
> +}
> +

[ snip ]

> @@ -2909,6 +3240,22 @@ int ext4_mb_init(struct super_block *sb)
> i++;
> } while (i < MB_NUM_ORDERS(sb));
>
> + sbi->s_mb_avg_fragment_size_root = RB_ROOT;
> + sbi->s_mb_largest_free_orders =
> + kmalloc_array(MB_NUM_ORDERS(sb), sizeof(struct list_head),
> + GFP_KERNEL);
> + if (!sbi->s_mb_largest_free_orders)
> + goto out;

Missing error code. ret = -ENOMEM;

> + sbi->s_mb_largest_free_orders_locks =
> + kmalloc_array(MB_NUM_ORDERS(sb), sizeof(rwlock_t),
> + GFP_KERNEL);
> + if (!sbi->s_mb_largest_free_orders_locks)
> + goto out;

ret = -ENOMEM;

> + for (i = 0; i < MB_NUM_ORDERS(sb); i++) {
> + INIT_LIST_HEAD(&sbi->s_mb_largest_free_orders[i]);
> + rwlock_init(&sbi->s_mb_largest_free_orders_locks[i]);
> + }
> + rwlock_init(&sbi->s_mb_rb_lock);
>
> spin_lock_init(&sbi->s_md_lock);
> sbi->s_mb_free_pending = 0;
> @@ -2961,6 +3308,10 @@ int ext4_mb_init(struct super_block *sb)
> spin_lock_init(&lg->lg_prealloc_lock);
> }
>
> + if (blk_queue_nonrot(bdev_get_queue(sb->s_bdev)))
> + sbi->s_mb_linear_limit = 0;
> + else
> + sbi->s_mb_linear_limit = MB_DEFAULT_LINEAR_LIMIT;
> /* init file for buddy data */
> ret = ext4_mb_init_backend(sb);
> if (ret != 0)
> @@ -2972,6 +3323,8 @@ int ext4_mb_init(struct super_block *sb)
> free_percpu(sbi->s_locality_groups);
> sbi->s_locality_groups = NULL;
> out:
> + kfree(sbi->s_mb_largest_free_orders);
> + kfree(sbi->s_mb_largest_free_orders_locks);
> kfree(sbi->s_mb_offsets);
> sbi->s_mb_offsets = NULL;
> kfree(sbi->s_mb_maxs);
> @@ -3028,6 +3381,7 @@ int ext4_mb_release(struct super_block *sb)
> kvfree(group_info);
> rcu_read_unlock();
> }
> + kfree(sbi->s_mb_largest_free_orders);


Add kfree(sbi->s_mb_largest_free_orders_locks);

> kfree(sbi->s_mb_offsets);
> kfree(sbi->s_mb_maxs);
> iput(sbi->s_buddy_cache);

regards,
dan carpenter

2021-03-22 15:34:32

by Artem Blagodarenko

[permalink] [raw]
Subject: Re: [PATCH v4 5/6] ext4: improve cr 0 / cr 1 group scanning

Hello Harshad.

Thanks again for your work.

Just want to remind that we have an optimisation in ext4_mb_normalize_request()
that increases request size based on file_offset + requested_size.
Can we use our knowledge about free 2^n ranges here to not increase this
“window” if there are no appropriate ranges?

Also I see a comment in ext4_mb_normalize_request()

"XXX: should this table be tunable?"

There is patch in Lustre FS that adds exact this tunable.

https://git.whamcloud.com/?p=fs/lustre-release.git;a=blob_plain;f=ldiskfs/kernel_patches/patches/rhel7.6/ext4-prealloc.patch;hb=HEAD

Do we still want such a tunable?

Best regards,
Artem Blagodarenko.


> On 15 Mar 2021, at 20:37, Harshad Shirwadkar <[email protected]> wrote:
>
> Instead of traversing through groups linearly, scan groups in specific
> orders at cr 0 and cr 1. At cr 0, we want to find groups that have the
> largest free order >= the order of the request. So, with this patch,
> we maintain lists for each possible order and insert each group into a
> list based on the largest free order in its buddy bitmap. During cr 0
> allocation, we traverse these lists in the increasing order of largest
> free orders. This allows us to find a group with the best available cr
> 0 match in constant time. If nothing can be found, we fallback to cr 1
> immediately.
>
> At CR1, the story is slightly different. We want to traverse in the
> order of increasing average fragment size. For CR1, we maintain a rb
> tree of groupinfos which is sorted by average fragment size. Instead
> of traversing linearly, at CR1, we traverse in the order of increasing
> average fragment size, starting at the most optimal group. This brings
> down cr 1 search complexity to log(num groups).
>
> For cr >= 2, we just perform the linear search as before. Also, in
> case of lock contention, we intermittently fallback to linear search
> even in CR 0 and CR 1 cases. This allows us to proceed during the
> allocation path even in case of high contention.
>
> There is an opportunity to do optimization at CR2 too. That's because
> at CR2 we only consider groups where bb_free counter (number of free
> blocks) is greater than the request extent size. That's left as future
> work.
>
> All the changes introduced in this patch are protected under a new
> mount option "mb_optimize_scan".
>
> Signed-off-by: Harshad Shirwadkar <[email protected]>
> Reported-by: kernel test robot <[email protected]>
> Reported-by: Dan Carpenter <[email protected]>
> ---
> fs/ext4/ext4.h | 19 ++-
> fs/ext4/mballoc.c | 376 ++++++++++++++++++++++++++++++++++++++++++++--
> fs/ext4/mballoc.h | 17 ++-
> fs/ext4/super.c | 28 +++-
> fs/ext4/sysfs.c | 2 +
> 5 files changed, 427 insertions(+), 15 deletions(-)
>
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 85eeeba3bca3..5930c8cb5159 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -162,7 +162,10 @@ enum SHIFT_DIRECTION {
> #define EXT4_MB_USE_RESERVED 0x2000
> /* Do strict check for free blocks while retrying block allocation */
> #define EXT4_MB_STRICT_CHECK 0x4000
> -
> +/* Large fragment size list lookup succeeded at least once for cr = 0 */
> +#define EXT4_MB_CR0_OPTIMIZED 0x8000
> +/* Avg fragment size rb tree lookup succeeded at least once for cr = 1 */
> +#define EXT4_MB_CR1_OPTIMIZED 0x00010000
> struct ext4_allocation_request {
> /* target inode for block we're allocating */
> struct inode *inode;
> @@ -1247,7 +1250,9 @@ struct ext4_inode_info {
> #define EXT4_MOUNT2_JOURNAL_FAST_COMMIT 0x00000010 /* Journal fast commit */
> #define EXT4_MOUNT2_DAX_NEVER 0x00000020 /* Do not allow Direct Access */
> #define EXT4_MOUNT2_DAX_INODE 0x00000040 /* For printing options only */
> -
> +#define EXT4_MOUNT2_MB_OPTIMIZE_SCAN 0x00000080 /* Optimize group
> + * scanning in mballoc
> + */
>
> #define clear_opt(sb, opt) EXT4_SB(sb)->s_mount_opt &= \
> ~EXT4_MOUNT_##opt
> @@ -1527,9 +1532,14 @@ struct ext4_sb_info {
> unsigned int s_mb_free_pending;
> struct list_head s_freed_data_list; /* List of blocks to be freed
> after commit completed */
> + struct rb_root s_mb_avg_fragment_size_root;
> + rwlock_t s_mb_rb_lock;
> + struct list_head *s_mb_largest_free_orders;
> + rwlock_t *s_mb_largest_free_orders_locks;
>
> /* tunables */
> unsigned long s_stripe;
> + unsigned int s_mb_linear_limit;
> unsigned int s_mb_stream_request;
> unsigned int s_mb_max_to_scan;
> unsigned int s_mb_min_to_scan;
> @@ -1553,6 +1563,8 @@ struct ext4_sb_info {
> atomic_t s_bal_goals; /* goal hits */
> atomic_t s_bal_breaks; /* too long searches */
> atomic_t s_bal_2orders; /* 2^order hits */
> + atomic_t s_bal_cr0_bad_suggestions;
> + atomic_t s_bal_cr1_bad_suggestions;
> atomic64_t s_bal_cX_groups_considered[4];
> atomic64_t s_bal_cX_hits[4];
> atomic64_t s_bal_cX_failed[4]; /* cX loop didn't find blocks */
> @@ -3309,11 +3321,14 @@ struct ext4_group_info {
> ext4_grpblk_t bb_free; /* total free blocks */
> ext4_grpblk_t bb_fragments; /* nr of freespace fragments */
> ext4_grpblk_t bb_largest_free_order;/* order of largest frag in BG */
> + ext4_group_t bb_group; /* Group number */
> struct list_head bb_prealloc_list;
> #ifdef DOUBLE_CHECK
> void *bb_bitmap;
> #endif
> struct rw_semaphore alloc_sem;
> + struct rb_node bb_avg_fragment_size_rb;
> + struct list_head bb_largest_free_order_node;
> ext4_grpblk_t bb_counters[]; /* Nr of free power-of-two-block
> * regions, index is order.
> * bb_counters[3] = 5 means
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 15127d815461..fb53ec1e1d37 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -127,11 +127,50 @@
> * smallest multiple of the stripe value (sbi->s_stripe) which is
> * greater than the default mb_group_prealloc.
> *
> + * If "mb_optimize_scan" mount option is set, we maintain in memory group info
> + * structures in two data structures:
> + *
> + * 1) Array of largest free order lists (sbi->s_mb_largest_free_orders)
> + *
> + * Locking: sbi->s_mb_largest_free_orders_locks(array of rw locks)
> + *
> + * This is an array of lists where the index in the array represents the
> + * largest free order in the buddy bitmap of the participating group infos of
> + * that list. So, there are exactly MB_NUM_ORDERS(sb) (which means total
> + * number of buddy bitmap orders possible) number of lists. Group-infos are
> + * placed in appropriate lists.
> + *
> + * 2) Average fragment size rb tree (sbi->s_mb_avg_fragment_size_root)
> + *
> + * Locking: sbi->s_mb_rb_lock (rwlock)
> + *
> + * This is a red black tree consisting of group infos and the tree is sorted
> + * by average fragment sizes (which is calculated as ext4_group_info->bb_free
> + * / ext4_group_info->bb_fragments).
> + *
> + * When "mb_optimize_scan" mount option is set, mballoc consults the above data
> + * structures to decide the order in which groups are to be traversed for
> + * fulfilling an allocation request.
> + *
> + * At CR = 0, we look for groups which have the largest_free_order >= the order
> + * of the request. We directly look at the largest free order list in the data
> + * structure (1) above where largest_free_order = order of the request. If that
> + * list is empty, we look at remaining list in the increasing order of
> + * largest_free_order. This allows us to perform CR = 0 lookup in O(1) time.
> + *
> + * At CR = 1, we only consider groups where average fragment size > request
> + * size. So, we lookup a group which has average fragment size just above or
> + * equal to request size using our rb tree (data structure 2) in O(log N) time.
> + *
> + * If "mb_optimize_scan" mount option is not set, mballoc traverses groups in
> + * linear order which requires O(N) search time for each CR 0 and CR 1 phase.
> + *
> * The regular allocator (using the buddy cache) supports a few tunables.
> *
> * /sys/fs/ext4/<partition>/mb_min_to_scan
> * /sys/fs/ext4/<partition>/mb_max_to_scan
> * /sys/fs/ext4/<partition>/mb_order2_req
> + * /sys/fs/ext4/<partition>/mb_linear_limit
> *
> * The regular allocator uses buddy scan only if the request len is power of
> * 2 blocks and the order of allocation is >= sbi->s_mb_order2_reqs. The
> @@ -149,6 +188,16 @@
> * can be used for allocation. ext4_mb_good_group explains how the groups are
> * checked.
> *
> + * When "mb_optimize_scan" is turned on, as mentioned above, the groups may not
> + * get traversed linearly. That may result in subsequent allocations being not
> + * close to each other. And so, the underlying device may get filled up in a
> + * non-linear fashion. While that may not matter on non-rotational devices, for
> + * rotational devices that may result in higher seek times. "mb_linear_limit"
> + * tells mballoc how many groups mballoc should search linearly before
> + * performing consulting above data structures for more efficient lookups. For
> + * non rotational devices, this value defaults to 0 and for rotational devices
> + * this is set to MB_DEFAULT_LINEAR_LIMIT.
> + *
> * Both the prealloc space are getting populated as above. So for the first
> * request we will hit the buddy cache which will result in this prealloc
> * space getting filled. The prealloc space is then later used for the
> @@ -299,6 +348,8 @@
> * - bitlock on a group (group)
> * - object (inode/locality) (object)
> * - per-pa lock (pa)
> + * - cr0 lists lock (cr0)
> + * - cr1 tree lock (cr1)
> *
> * Paths:
> * - new pa
> @@ -328,6 +379,9 @@
> * group
> * object
> *
> + * - allocation path (ext4_mb_regular_allocator)
> + * group
> + * cr0/cr1
> */
> static struct kmem_cache *ext4_pspace_cachep;
> static struct kmem_cache *ext4_ac_cachep;
> @@ -351,6 +405,9 @@ static void ext4_mb_generate_from_freelist(struct super_block *sb, void *bitmap,
> ext4_group_t group);
> static void ext4_mb_new_preallocation(struct ext4_allocation_context *ac);
>
> +static bool ext4_mb_good_group(struct ext4_allocation_context *ac,
> + ext4_group_t group, int cr);
> +
> /*
> * The algorithm using this percpu seq counter goes below:
> * 1. We sample the percpu discard_pa_seq counter before trying for block
> @@ -744,6 +801,251 @@ static void ext4_mb_mark_free_simple(struct super_block *sb,
> }
> }
>
> +static void ext4_mb_rb_insert(struct rb_root *root, struct rb_node *new,
> + int (*cmp)(struct rb_node *, struct rb_node *))
> +{
> + struct rb_node **iter = &root->rb_node, *parent = NULL;
> +
> + while (*iter) {
> + parent = *iter;
> + if (cmp(new, *iter))
> + iter = &((*iter)->rb_left);
> + else
> + iter = &((*iter)->rb_right);
> + }
> +
> + rb_link_node(new, parent, iter);
> + rb_insert_color(new, root);
> +}
> +
> +static int
> +ext4_mb_avg_fragment_size_cmp(struct rb_node *rb1, struct rb_node *rb2)
> +{
> + struct ext4_group_info *grp1 = rb_entry(rb1,
> + struct ext4_group_info,
> + bb_avg_fragment_size_rb);
> + struct ext4_group_info *grp2 = rb_entry(rb2,
> + struct ext4_group_info,
> + bb_avg_fragment_size_rb);
> + int num_frags_1, num_frags_2;
> +
> + num_frags_1 = grp1->bb_fragments ?
> + grp1->bb_free / grp1->bb_fragments : 0;
> + num_frags_2 = grp2->bb_fragments ?
> + grp2->bb_free / grp2->bb_fragments : 0;
> +
> + return (num_frags_1 < num_frags_2);
> +}
> +
> +/*
> + * Reinsert grpinfo into the avg_fragment_size tree with new average
> + * fragment size.
> + */
> +static void
> +mb_update_avg_fragment_size(struct super_block *sb, struct ext4_group_info *grp)
> +{
> + struct ext4_sb_info *sbi = EXT4_SB(sb);
> +
> + if (!test_opt2(sb, MB_OPTIMIZE_SCAN) || grp->bb_free == 0)
> + return;
> +
> + write_lock(&sbi->s_mb_rb_lock);
> + if (!RB_EMPTY_NODE(&grp->bb_avg_fragment_size_rb)) {
> + rb_erase(&grp->bb_avg_fragment_size_rb,
> + &sbi->s_mb_avg_fragment_size_root);
> + RB_CLEAR_NODE(&grp->bb_avg_fragment_size_rb);
> + }
> +
> + ext4_mb_rb_insert(&sbi->s_mb_avg_fragment_size_root,
> + &grp->bb_avg_fragment_size_rb,
> + ext4_mb_avg_fragment_size_cmp);
> + write_unlock(&sbi->s_mb_rb_lock);
> +}
> +
> +/*
> + * Choose next group by traversing largest_free_order lists. Return 0 if next
> + * group was selected optimally. Return 1 if next group was not selected
> + * optimally. Updates *new_cr if cr level needs an update.
> + */
> +static int ext4_mb_choose_next_group_cr0(struct ext4_allocation_context *ac,
> + int *new_cr, ext4_group_t *group, ext4_group_t ngroups)
> +{
> + struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
> + struct ext4_group_info *iter, *grp;
> + int i;
> +
> + if (ac->ac_status == AC_STATUS_FOUND)
> + return 1;
> +
> + if (unlikely(sbi->s_mb_stats && ac->ac_flags & EXT4_MB_CR0_OPTIMIZED))
> + atomic_inc(&sbi->s_bal_cr0_bad_suggestions);
> +
> + grp = NULL;
> + for (i = ac->ac_2order; i < MB_NUM_ORDERS(ac->ac_sb); i++) {
> + if (list_empty(&sbi->s_mb_largest_free_orders[i]))
> + continue;
> + read_lock(&sbi->s_mb_largest_free_orders_locks[i]);
> + if (list_empty(&sbi->s_mb_largest_free_orders[i])) {
> + read_unlock(&sbi->s_mb_largest_free_orders_locks[i]);
> + continue;
> + }
> + grp = NULL;
> + list_for_each_entry(iter, &sbi->s_mb_largest_free_orders[i],
> + bb_largest_free_order_node) {
> + if (sbi->s_mb_stats)
> + atomic64_inc(&sbi->s_bal_cX_groups_considered[0]);
> + if (likely(ext4_mb_good_group(ac, iter->bb_group, 0))) {
> + grp = iter;
> + break;
> + }
> + }
> + read_unlock(&sbi->s_mb_largest_free_orders_locks[i]);
> + if (grp)
> + break;
> + }
> +
> + if (!grp) {
> + /* Increment cr and search again */
> + *new_cr = 1;
> + } else {
> + *group = grp->bb_group;
> + ac->ac_last_optimal_group = *group;
> + ac->ac_flags |= EXT4_MB_CR0_OPTIMIZED;
> + }
> + return 0;
> +}
> +
> +/*
> + * Choose next group by traversing average fragment size tree. Return 0 if next
> + * group was selected optimally. Return 1 if next group could not selected
> + * optimally (due to lock contention). Updates *new_cr if cr lvel needs an
> + * update.
> + */
> +static int ext4_mb_choose_next_group_cr1(struct ext4_allocation_context *ac,
> + int *new_cr, ext4_group_t *group, ext4_group_t ngroups)
> +{
> + struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
> + int avg_fragment_size, best_so_far;
> + struct rb_node *node, *found;
> + struct ext4_group_info *grp;
> +
> + /*
> + * If there is contention on the lock, instead of waiting for the lock
> + * to become available, just continue searching lineraly. We'll resume
> + * our rb tree search later starting at ac->ac_last_optimal_group.
> + */
> + if (!read_trylock(&sbi->s_mb_rb_lock))
> + return 1;
> +
> + if (unlikely(ac->ac_flags & EXT4_MB_CR1_OPTIMIZED)) {
> + if (sbi->s_mb_stats)
> + atomic_inc(&sbi->s_bal_cr1_bad_suggestions);
> + /* We have found something at CR 1 in the past */
> + grp = ext4_get_group_info(ac->ac_sb, ac->ac_last_optimal_group);
> + for (found = rb_next(&grp->bb_avg_fragment_size_rb); found != NULL;
> + found = rb_next(found)) {
> + grp = rb_entry(found, struct ext4_group_info,
> + bb_avg_fragment_size_rb);
> + if (sbi->s_mb_stats)
> + atomic64_inc(&sbi->s_bal_cX_groups_considered[1]);
> + if (likely(ext4_mb_good_group(ac, grp->bb_group, 1)))
> + break;
> + }
> +
> + goto done;
> + }
> +
> + node = sbi->s_mb_avg_fragment_size_root.rb_node;
> + best_so_far = 0;
> + found = NULL;
> +
> + while (node) {
> + grp = rb_entry(node, struct ext4_group_info,
> + bb_avg_fragment_size_rb);
> + avg_fragment_size = 0;
> + /*
> + * Perform this check without locking, we'll lock later to confirm.
> + */
> + if (ext4_mb_good_group(ac, grp->bb_group, 1)) {
> + avg_fragment_size = grp->bb_fragments ?
> + grp->bb_free / grp->bb_fragments : 0;
> + if (!best_so_far || avg_fragment_size < best_so_far) {
> + best_so_far = avg_fragment_size;
> + found = node;
> + }
> + }
> + if (avg_fragment_size > ac->ac_g_ex.fe_len)
> + node = node->rb_right;
> + else
> + node = node->rb_left;
> + }
> +
> +done:
> + if (found) {
> + grp = rb_entry(found, struct ext4_group_info,
> + bb_avg_fragment_size_rb);
> + *group = grp->bb_group;
> + ac->ac_flags |= EXT4_MB_CR1_OPTIMIZED;
> + } else {
> + *new_cr = 2;
> + }
> +
> + read_unlock(&sbi->s_mb_rb_lock);
> + ac->ac_last_optimal_group = *group;
> + return 0;
> +}
> +
> +/*
> + * ext4_mb_choose_next_group: choose next group for allocation.
> + *
> + * @ac Allocation Context
> + * @new_cr This is an output parameter. If the there is no good group
> + * available at current CR level, this field is updated to indicate
> + * the new cr level that should be used.
> + * @group This is an input / output parameter. As an input it indicates the
> + * last group used for allocation. As output, this field indicates
> + * the next group that should be used.
> + * @ngroups Total number of groups
> + */
> +static void ext4_mb_choose_next_group(struct ext4_allocation_context *ac,
> + int *new_cr, ext4_group_t *group, ext4_group_t ngroups)
> +{
> + int ret;
> +
> + *new_cr = ac->ac_criteria;
> +
> + if (!test_opt2(ac->ac_sb, MB_OPTIMIZE_SCAN) ||
> + *new_cr >= 2 ||
> + !ext4_test_inode_flag(ac->ac_inode, EXT4_INODE_EXTENTS))
> + goto inc_and_return;
> +
> + if (ac->ac_groups_linear_remaining) {
> + ac->ac_groups_linear_remaining--;
> + goto inc_and_return;
> + }
> +
> + if (*new_cr == 0) {
> + ret = ext4_mb_choose_next_group_cr0(ac, new_cr, group, ngroups);
> + if (ret)
> + goto inc_and_return;
> + }
> + if (*new_cr == 1) {
> + ret = ext4_mb_choose_next_group_cr1(ac, new_cr, group, ngroups);
> + if (ret)
> + goto inc_and_return;
> + }
> + return;
> +
> +inc_and_return:
> + /*
> + * Artificially restricted ngroups for non-extent
> + * files makes group > ngroups possible on first loop.
> + */
> + *group = *group + 1;
> + if (*group >= ngroups)
> + *group = 0;
> +}
> +
> /*
> * Cache the order of the largest free extent we have available in this block
> * group.
> @@ -751,18 +1053,33 @@ static void ext4_mb_mark_free_simple(struct super_block *sb,
> static void
> mb_set_largest_free_order(struct super_block *sb, struct ext4_group_info *grp)
> {
> + struct ext4_sb_info *sbi = EXT4_SB(sb);
> int i;
> - int bits;
>
> + if (test_opt2(sb, MB_OPTIMIZE_SCAN) && grp->bb_largest_free_order >= 0) {
> + write_lock(&sbi->s_mb_largest_free_orders_locks[
> + grp->bb_largest_free_order]);
> + list_del_init(&grp->bb_largest_free_order_node);
> + write_unlock(&sbi->s_mb_largest_free_orders_locks[
> + grp->bb_largest_free_order]);
> + }
> grp->bb_largest_free_order = -1; /* uninit */
>
> - bits = MB_NUM_ORDERS(sb) - 1;
> - for (i = bits; i >= 0; i--) {
> + for (i = MB_NUM_ORDERS(sb) - 1; i >= 0; i--) {
> if (grp->bb_counters[i] > 0) {
> grp->bb_largest_free_order = i;
> break;
> }
> }
> + if (test_opt2(sb, MB_OPTIMIZE_SCAN) &&
> + grp->bb_largest_free_order >= 0 && grp->bb_free) {
> + write_lock(&sbi->s_mb_largest_free_orders_locks[
> + grp->bb_largest_free_order]);
> + list_add_tail(&grp->bb_largest_free_order_node,
> + &sbi->s_mb_largest_free_orders[grp->bb_largest_free_order]);
> + write_unlock(&sbi->s_mb_largest_free_orders_locks[
> + grp->bb_largest_free_order]);
> + }
> }
>
> static noinline_for_stack
> @@ -818,6 +1135,7 @@ void ext4_mb_generate_buddy(struct super_block *sb,
> period = get_cycles() - period;
> atomic_inc(&sbi->s_mb_buddies_generated);
> atomic64_add(period, &sbi->s_mb_generation_time);
> + mb_update_avg_fragment_size(sb, grp);
> }
>
> /* The buddy information is attached the buddy cache inode
> @@ -1517,6 +1835,7 @@ static void mb_free_blocks(struct inode *inode, struct ext4_buddy *e4b,
>
> done:
> mb_set_largest_free_order(sb, e4b->bd_info);
> + mb_update_avg_fragment_size(sb, e4b->bd_info);
> mb_check_buddy(e4b);
> }
>
> @@ -1653,6 +1972,7 @@ static int mb_mark_used(struct ext4_buddy *e4b, struct ext4_free_extent *ex)
> }
> mb_set_largest_free_order(e4b->bd_sb, e4b->bd_info);
>
> + mb_update_avg_fragment_size(e4b->bd_sb, e4b->bd_info);
> ext4_set_bits(e4b->bd_bitmap, ex->fe_start, len0);
> mb_check_buddy(e4b);
>
> @@ -2347,17 +2667,21 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
> * from the goal value specified
> */
> group = ac->ac_g_ex.fe_group;
> + ac->ac_last_optimal_group = group;
> + ac->ac_groups_linear_remaining = sbi->s_mb_linear_limit;
> prefetch_grp = group;
>
> - for (i = 0; i < ngroups; group++, i++) {
> - int ret = 0;
> + for (i = 0; i < ngroups; i++) {
> + int ret = 0, new_cr;
> +
> cond_resched();
> - /*
> - * Artificially restricted ngroups for non-extent
> - * files makes group > ngroups possible on first loop.
> - */
> - if (group >= ngroups)
> - group = 0;
> +
> + ext4_mb_choose_next_group(ac, &new_cr, &group, ngroups);
> +
> + if (new_cr != cr) {
> + cr = new_cr;
> + goto repeat;
> + }
>
> /*
> * Batch reads of the block allocation bitmaps
> @@ -2578,6 +2902,8 @@ int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset)
> atomic64_read(&sbi->s_bal_cX_groups_considered[0]));
> seq_printf(seq, "\t\tuseless_loops: %llu\n",
> atomic64_read(&sbi->s_bal_cX_failed[0]));
> + seq_printf(seq, "\t\tbad_suggestions: %u\n",
> + atomic_read(&sbi->s_bal_cr0_bad_suggestions));
>
> seq_puts(seq, "\tcr1_stats:\n");
> seq_printf(seq, "\t\thits: %llu\n", atomic64_read(&sbi->s_bal_cX_hits[1]));
> @@ -2585,6 +2911,8 @@ int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset)
> atomic64_read(&sbi->s_bal_cX_groups_considered[1]));
> seq_printf(seq, "\t\tuseless_loops: %llu\n",
> atomic64_read(&sbi->s_bal_cX_failed[1]));
> + seq_printf(seq, "\t\tbad_suggestions: %u\n",
> + atomic_read(&sbi->s_bal_cr1_bad_suggestions));
>
> seq_puts(seq, "\tcr2_stats:\n");
> seq_printf(seq, "\t\thits: %llu\n", atomic64_read(&sbi->s_bal_cX_hits[2]));
> @@ -2719,7 +3047,10 @@ int ext4_mb_add_groupinfo(struct super_block *sb, ext4_group_t group,
> INIT_LIST_HEAD(&meta_group_info[i]->bb_prealloc_list);
> init_rwsem(&meta_group_info[i]->alloc_sem);
> meta_group_info[i]->bb_free_root = RB_ROOT;
> + INIT_LIST_HEAD(&meta_group_info[i]->bb_largest_free_order_node);
> + RB_CLEAR_NODE(&meta_group_info[i]->bb_avg_fragment_size_rb);
> meta_group_info[i]->bb_largest_free_order = -1; /* uninit */
> + meta_group_info[i]->bb_group = group;
>
> mb_group_bb_bitmap_alloc(sb, meta_group_info[i], group);
> return 0;
> @@ -2909,6 +3240,22 @@ int ext4_mb_init(struct super_block *sb)
> i++;
> } while (i < MB_NUM_ORDERS(sb));
>
> + sbi->s_mb_avg_fragment_size_root = RB_ROOT;
> + sbi->s_mb_largest_free_orders =
> + kmalloc_array(MB_NUM_ORDERS(sb), sizeof(struct list_head),
> + GFP_KERNEL);
> + if (!sbi->s_mb_largest_free_orders)
> + goto out;
> + sbi->s_mb_largest_free_orders_locks =
> + kmalloc_array(MB_NUM_ORDERS(sb), sizeof(rwlock_t),
> + GFP_KERNEL);
> + if (!sbi->s_mb_largest_free_orders_locks)
> + goto out;
> + for (i = 0; i < MB_NUM_ORDERS(sb); i++) {
> + INIT_LIST_HEAD(&sbi->s_mb_largest_free_orders[i]);
> + rwlock_init(&sbi->s_mb_largest_free_orders_locks[i]);
> + }
> + rwlock_init(&sbi->s_mb_rb_lock);
>
> spin_lock_init(&sbi->s_md_lock);
> sbi->s_mb_free_pending = 0;
> @@ -2961,6 +3308,10 @@ int ext4_mb_init(struct super_block *sb)
> spin_lock_init(&lg->lg_prealloc_lock);
> }
>
> + if (blk_queue_nonrot(bdev_get_queue(sb->s_bdev)))
> + sbi->s_mb_linear_limit = 0;
> + else
> + sbi->s_mb_linear_limit = MB_DEFAULT_LINEAR_LIMIT;
> /* init file for buddy data */
> ret = ext4_mb_init_backend(sb);
> if (ret != 0)
> @@ -2972,6 +3323,8 @@ int ext4_mb_init(struct super_block *sb)
> free_percpu(sbi->s_locality_groups);
> sbi->s_locality_groups = NULL;
> out:
> + kfree(sbi->s_mb_largest_free_orders);
> + kfree(sbi->s_mb_largest_free_orders_locks);
> kfree(sbi->s_mb_offsets);
> sbi->s_mb_offsets = NULL;
> kfree(sbi->s_mb_maxs);
> @@ -3028,6 +3381,7 @@ int ext4_mb_release(struct super_block *sb)
> kvfree(group_info);
> rcu_read_unlock();
> }
> + kfree(sbi->s_mb_largest_free_orders);
> kfree(sbi->s_mb_offsets);
> kfree(sbi->s_mb_maxs);
> iput(sbi->s_buddy_cache);
> diff --git a/fs/ext4/mballoc.h b/fs/ext4/mballoc.h
> index 68111a10cfee..02585e3cbcad 100644
> --- a/fs/ext4/mballoc.h
> +++ b/fs/ext4/mballoc.h
> @@ -78,6 +78,18 @@
> */
> #define MB_DEFAULT_MAX_INODE_PREALLOC 512
>
> +/*
> + * Number of groups to search linearly before performing group scanning
> + * optimization.
> + */
> +#define MB_DEFAULT_LINEAR_LIMIT 4
> +
> +/*
> + * Minimum number of groups that should be present in the file system to perform
> + * group scanning optimizations.
> + */
> +#define MB_DEFAULT_LINEAR_SCAN_THRESHOLD 16
> +
> /*
> * Number of valid buddy orders
> */
> @@ -166,11 +178,14 @@ struct ext4_allocation_context {
> /* copy of the best found extent taken before preallocation efforts */
> struct ext4_free_extent ac_f_ex;
>
> + ext4_group_t ac_last_optimal_group;
> + __u32 ac_groups_considered;
> + __u32 ac_flags; /* allocation hints */
> __u16 ac_groups_scanned;
> + __u16 ac_groups_linear_remaining;
> __u16 ac_found;
> __u16 ac_tail;
> __u16 ac_buddy;
> - __u16 ac_flags; /* allocation hints */
> __u8 ac_status;
> __u8 ac_criteria;
> __u8 ac_2order; /* if request is to allocate 2^N blocks and
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 0491e7a6b04c..5b973f037298 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -1687,7 +1687,7 @@ enum {
> Opt_dioread_nolock, Opt_dioread_lock,
> Opt_discard, Opt_nodiscard, Opt_init_itable, Opt_noinit_itable,
> Opt_max_dir_size_kb, Opt_nojournal_checksum, Opt_nombcache,
> - Opt_prefetch_block_bitmaps,
> + Opt_prefetch_block_bitmaps, Opt_mb_optimize_scan,
> #ifdef CONFIG_EXT4_DEBUG
> Opt_fc_debug_max_replay, Opt_fc_debug_force
> #endif
> @@ -1788,6 +1788,7 @@ static const match_table_t tokens = {
> {Opt_nombcache, "nombcache"},
> {Opt_nombcache, "no_mbcache"}, /* for backward compatibility */
> {Opt_prefetch_block_bitmaps, "prefetch_block_bitmaps"},
> + {Opt_mb_optimize_scan, "mb_optimize_scan=%d"},
> {Opt_removed, "check=none"}, /* mount option from ext2/3 */
> {Opt_removed, "nocheck"}, /* mount option from ext2/3 */
> {Opt_removed, "reservation"}, /* mount option from ext2/3 */
> @@ -1820,6 +1821,8 @@ static ext4_fsblk_t get_sb_block(void **data)
> }
>
> #define DEFAULT_JOURNAL_IOPRIO (IOPRIO_PRIO_VALUE(IOPRIO_CLASS_BE, 3))
> +#define DEFAULT_MB_OPTIMIZE_SCAN (-1)
> +
> static const char deprecated_msg[] =
> "Mount option \"%s\" will be removed by %s\n"
> "Contact [email protected] if you think we should keep it.\n";
> @@ -2008,6 +2011,7 @@ static const struct mount_opts {
> {Opt_nombcache, EXT4_MOUNT_NO_MBCACHE, MOPT_SET},
> {Opt_prefetch_block_bitmaps, EXT4_MOUNT_PREFETCH_BLOCK_BITMAPS,
> MOPT_SET},
> + {Opt_mb_optimize_scan, EXT4_MOUNT2_MB_OPTIMIZE_SCAN, MOPT_GTE0},
> #ifdef CONFIG_EXT4_DEBUG
> {Opt_fc_debug_force, EXT4_MOUNT2_JOURNAL_FAST_COMMIT,
> MOPT_SET | MOPT_2 | MOPT_EXT4_ONLY},
> @@ -2092,6 +2096,7 @@ static int ext4_set_test_dummy_encryption(struct super_block *sb,
> struct ext4_parsed_options {
> unsigned long journal_devnum;
> unsigned int journal_ioprio;
> + int mb_optimize_scan;
> };
>
> static int handle_mount_opt(struct super_block *sb, char *opt, int token,
> @@ -2388,6 +2393,13 @@ static int handle_mount_opt(struct super_block *sb, char *opt, int token,
> sbi->s_mount_opt |= m->mount_opt;
> } else if (token == Opt_data_err_ignore) {
> sbi->s_mount_opt &= ~m->mount_opt;
> + } else if (token == Opt_mb_optimize_scan) {
> + if (arg != 0 && arg != 1) {
> + ext4_msg(sb, KERN_WARNING,
> + "mb_optimize_scan should be set to 0 or 1.");
> + return -1;
> + }
> + parsed_opts->mb_optimize_scan = arg;
> } else {
> if (!args->from)
> arg = 1;
> @@ -4034,6 +4046,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> /* Set defaults for the variables that will be set during parsing */
> parsed_opts.journal_ioprio = DEFAULT_JOURNAL_IOPRIO;
> parsed_opts.journal_devnum = 0;
> + parsed_opts.mb_optimize_scan = DEFAULT_MB_OPTIMIZE_SCAN;
>
> if ((data && !orig_data) || !sbi)
> goto out_free_base;
> @@ -4984,6 +4997,19 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> ext4_fc_replay_cleanup(sb);
>
> ext4_ext_init(sb);
> +
> + /*
> + * Enable optimize_scan if number of groups is > threshold. This can be
> + * turned off by passing "mb_optimize_scan=0". This can also be
> + * turned on forcefully by passing "mb_optimize_scan=1".
> + */
> + if (parsed_opts.mb_optimize_scan == 1)
> + set_opt2(sb, MB_OPTIMIZE_SCAN);
> + else if (parsed_opts.mb_optimize_scan == 0)
> + clear_opt2(sb, MB_OPTIMIZE_SCAN);
> + else if (sbi->s_groups_count >= MB_DEFAULT_LINEAR_SCAN_THRESHOLD)
> + set_opt2(sb, MB_OPTIMIZE_SCAN);
> +
> err = ext4_mb_init(sb);
> if (err) {
> ext4_msg(sb, KERN_ERR, "failed to initialize mballoc (%d)",
> diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c
> index 59ca9d73b42f..16b8a838f631 100644
> --- a/fs/ext4/sysfs.c
> +++ b/fs/ext4/sysfs.c
> @@ -213,6 +213,7 @@ EXT4_RW_ATTR_SBI_UI(mb_order2_req, s_mb_order2_reqs);
> EXT4_RW_ATTR_SBI_UI(mb_stream_req, s_mb_stream_request);
> EXT4_RW_ATTR_SBI_UI(mb_group_prealloc, s_mb_group_prealloc);
> EXT4_RW_ATTR_SBI_UI(mb_max_inode_prealloc, s_mb_max_inode_prealloc);
> +EXT4_RW_ATTR_SBI_UI(mb_linear_limit, s_mb_linear_limit);
> EXT4_RW_ATTR_SBI_UI(extent_max_zeroout_kb, s_extent_max_zeroout_kb);
> EXT4_ATTR(trigger_fs_error, 0200, trigger_test_error);
> EXT4_RW_ATTR_SBI_UI(err_ratelimit_interval_ms, s_err_ratelimit_state.interval);
> @@ -260,6 +261,7 @@ static struct attribute *ext4_attrs[] = {
> ATTR_LIST(mb_stream_req),
> ATTR_LIST(mb_group_prealloc),
> ATTR_LIST(mb_max_inode_prealloc),
> + ATTR_LIST(mb_linear_limit),
> ATTR_LIST(max_writeback_mb_bump),
> ATTR_LIST(extent_max_zeroout_kb),
> ATTR_LIST(trigger_fs_error),
> --
> 2.31.0.rc2.261.g7f71774620-goog
>

2021-03-22 17:27:19

by Harshad Shirwadkar

[permalink] [raw]
Subject: Re: [PATCH v4 5/6] ext4: improve cr 0 / cr 1 group scanning

Thanks Dan and Artem for the feedback.

Dan, I'll add fixes you mentioned in the next version.

Artem, I think it would be useful to have this optimization in and
also yes, with the new data structures, we probably can do better
guessing of the final size. But, since this patchset already
introduces significant changes to the allocator and also has grown in
overall size, I think let's first get in these changes and then
re-implement the patch you shared as a separate patch on top of the
dev tree.

Thanks,
Harshad


On Mon, Mar 22, 2021 at 8:33 AM Благодаренко Артём
<[email protected]> wrote:
>
> Hello Harshad.
>
> Thanks again for your work.
>
> Just want to remind that we have an optimisation in ext4_mb_normalize_request()
> that increases request size based on file_offset + requested_size.
> Can we use our knowledge about free 2^n ranges here to not increase this
> “window” if there are no appropriate ranges?
>
> Also I see a comment in ext4_mb_normalize_request()
>
> "XXX: should this table be tunable?"
>
> There is patch in Lustre FS that adds exact this tunable.
>
> https://git.whamcloud.com/?p=fs/lustre-release.git;a=blob_plain;f=ldiskfs/kernel_patches/patches/rhel7.6/ext4-prealloc.patch;hb=HEAD
>
> Do we still want such a tunable?
>
> Best regards,
> Artem Blagodarenko.
>
>
> > On 15 Mar 2021, at 20:37, Harshad Shirwadkar <[email protected]> wrote:
> >
> > Instead of traversing through groups linearly, scan groups in specific
> > orders at cr 0 and cr 1. At cr 0, we want to find groups that have the
> > largest free order >= the order of the request. So, with this patch,
> > we maintain lists for each possible order and insert each group into a
> > list based on the largest free order in its buddy bitmap. During cr 0
> > allocation, we traverse these lists in the increasing order of largest
> > free orders. This allows us to find a group with the best available cr
> > 0 match in constant time. If nothing can be found, we fallback to cr 1
> > immediately.
> >
> > At CR1, the story is slightly different. We want to traverse in the
> > order of increasing average fragment size. For CR1, we maintain a rb
> > tree of groupinfos which is sorted by average fragment size. Instead
> > of traversing linearly, at CR1, we traverse in the order of increasing
> > average fragment size, starting at the most optimal group. This brings
> > down cr 1 search complexity to log(num groups).
> >
> > For cr >= 2, we just perform the linear search as before. Also, in
> > case of lock contention, we intermittently fallback to linear search
> > even in CR 0 and CR 1 cases. This allows us to proceed during the
> > allocation path even in case of high contention.
> >
> > There is an opportunity to do optimization at CR2 too. That's because
> > at CR2 we only consider groups where bb_free counter (number of free
> > blocks) is greater than the request extent size. That's left as future
> > work.
> >
> > All the changes introduced in this patch are protected under a new
> > mount option "mb_optimize_scan".
> >
> > Signed-off-by: Harshad Shirwadkar <[email protected]>
> > Reported-by: kernel test robot <[email protected]>
> > Reported-by: Dan Carpenter <[email protected]>
> > ---
> > fs/ext4/ext4.h | 19 ++-
> > fs/ext4/mballoc.c | 376 ++++++++++++++++++++++++++++++++++++++++++++--
> > fs/ext4/mballoc.h | 17 ++-
> > fs/ext4/super.c | 28 +++-
> > fs/ext4/sysfs.c | 2 +
> > 5 files changed, 427 insertions(+), 15 deletions(-)
> >
> > diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> > index 85eeeba3bca3..5930c8cb5159 100644
> > --- a/fs/ext4/ext4.h
> > +++ b/fs/ext4/ext4.h
> > @@ -162,7 +162,10 @@ enum SHIFT_DIRECTION {
> > #define EXT4_MB_USE_RESERVED 0x2000
> > /* Do strict check for free blocks while retrying block allocation */
> > #define EXT4_MB_STRICT_CHECK 0x4000
> > -
> > +/* Large fragment size list lookup succeeded at least once for cr = 0 */
> > +#define EXT4_MB_CR0_OPTIMIZED 0x8000
> > +/* Avg fragment size rb tree lookup succeeded at least once for cr = 1 */
> > +#define EXT4_MB_CR1_OPTIMIZED 0x00010000
> > struct ext4_allocation_request {
> > /* target inode for block we're allocating */
> > struct inode *inode;
> > @@ -1247,7 +1250,9 @@ struct ext4_inode_info {
> > #define EXT4_MOUNT2_JOURNAL_FAST_COMMIT 0x00000010 /* Journal fast commit */
> > #define EXT4_MOUNT2_DAX_NEVER 0x00000020 /* Do not allow Direct Access */
> > #define EXT4_MOUNT2_DAX_INODE 0x00000040 /* For printing options only */
> > -
> > +#define EXT4_MOUNT2_MB_OPTIMIZE_SCAN 0x00000080 /* Optimize group
> > + * scanning in mballoc
> > + */
> >
> > #define clear_opt(sb, opt) EXT4_SB(sb)->s_mount_opt &= \
> > ~EXT4_MOUNT_##opt
> > @@ -1527,9 +1532,14 @@ struct ext4_sb_info {
> > unsigned int s_mb_free_pending;
> > struct list_head s_freed_data_list; /* List of blocks to be freed
> > after commit completed */
> > + struct rb_root s_mb_avg_fragment_size_root;
> > + rwlock_t s_mb_rb_lock;
> > + struct list_head *s_mb_largest_free_orders;
> > + rwlock_t *s_mb_largest_free_orders_locks;
> >
> > /* tunables */
> > unsigned long s_stripe;
> > + unsigned int s_mb_linear_limit;
> > unsigned int s_mb_stream_request;
> > unsigned int s_mb_max_to_scan;
> > unsigned int s_mb_min_to_scan;
> > @@ -1553,6 +1563,8 @@ struct ext4_sb_info {
> > atomic_t s_bal_goals; /* goal hits */
> > atomic_t s_bal_breaks; /* too long searches */
> > atomic_t s_bal_2orders; /* 2^order hits */
> > + atomic_t s_bal_cr0_bad_suggestions;
> > + atomic_t s_bal_cr1_bad_suggestions;
> > atomic64_t s_bal_cX_groups_considered[4];
> > atomic64_t s_bal_cX_hits[4];
> > atomic64_t s_bal_cX_failed[4]; /* cX loop didn't find blocks */
> > @@ -3309,11 +3321,14 @@ struct ext4_group_info {
> > ext4_grpblk_t bb_free; /* total free blocks */
> > ext4_grpblk_t bb_fragments; /* nr of freespace fragments */
> > ext4_grpblk_t bb_largest_free_order;/* order of largest frag in BG */
> > + ext4_group_t bb_group; /* Group number */
> > struct list_head bb_prealloc_list;
> > #ifdef DOUBLE_CHECK
> > void *bb_bitmap;
> > #endif
> > struct rw_semaphore alloc_sem;
> > + struct rb_node bb_avg_fragment_size_rb;
> > + struct list_head bb_largest_free_order_node;
> > ext4_grpblk_t bb_counters[]; /* Nr of free power-of-two-block
> > * regions, index is order.
> > * bb_counters[3] = 5 means
> > diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> > index 15127d815461..fb53ec1e1d37 100644
> > --- a/fs/ext4/mballoc.c
> > +++ b/fs/ext4/mballoc.c
> > @@ -127,11 +127,50 @@
> > * smallest multiple of the stripe value (sbi->s_stripe) which is
> > * greater than the default mb_group_prealloc.
> > *
> > + * If "mb_optimize_scan" mount option is set, we maintain in memory group info
> > + * structures in two data structures:
> > + *
> > + * 1) Array of largest free order lists (sbi->s_mb_largest_free_orders)
> > + *
> > + * Locking: sbi->s_mb_largest_free_orders_locks(array of rw locks)
> > + *
> > + * This is an array of lists where the index in the array represents the
> > + * largest free order in the buddy bitmap of the participating group infos of
> > + * that list. So, there are exactly MB_NUM_ORDERS(sb) (which means total
> > + * number of buddy bitmap orders possible) number of lists. Group-infos are
> > + * placed in appropriate lists.
> > + *
> > + * 2) Average fragment size rb tree (sbi->s_mb_avg_fragment_size_root)
> > + *
> > + * Locking: sbi->s_mb_rb_lock (rwlock)
> > + *
> > + * This is a red black tree consisting of group infos and the tree is sorted
> > + * by average fragment sizes (which is calculated as ext4_group_info->bb_free
> > + * / ext4_group_info->bb_fragments).
> > + *
> > + * When "mb_optimize_scan" mount option is set, mballoc consults the above data
> > + * structures to decide the order in which groups are to be traversed for
> > + * fulfilling an allocation request.
> > + *
> > + * At CR = 0, we look for groups which have the largest_free_order >= the order
> > + * of the request. We directly look at the largest free order list in the data
> > + * structure (1) above where largest_free_order = order of the request. If that
> > + * list is empty, we look at remaining list in the increasing order of
> > + * largest_free_order. This allows us to perform CR = 0 lookup in O(1) time.
> > + *
> > + * At CR = 1, we only consider groups where average fragment size > request
> > + * size. So, we lookup a group which has average fragment size just above or
> > + * equal to request size using our rb tree (data structure 2) in O(log N) time.
> > + *
> > + * If "mb_optimize_scan" mount option is not set, mballoc traverses groups in
> > + * linear order which requires O(N) search time for each CR 0 and CR 1 phase.
> > + *
> > * The regular allocator (using the buddy cache) supports a few tunables.
> > *
> > * /sys/fs/ext4/<partition>/mb_min_to_scan
> > * /sys/fs/ext4/<partition>/mb_max_to_scan
> > * /sys/fs/ext4/<partition>/mb_order2_req
> > + * /sys/fs/ext4/<partition>/mb_linear_limit
> > *
> > * The regular allocator uses buddy scan only if the request len is power of
> > * 2 blocks and the order of allocation is >= sbi->s_mb_order2_reqs. The
> > @@ -149,6 +188,16 @@
> > * can be used for allocation. ext4_mb_good_group explains how the groups are
> > * checked.
> > *
> > + * When "mb_optimize_scan" is turned on, as mentioned above, the groups may not
> > + * get traversed linearly. That may result in subsequent allocations being not
> > + * close to each other. And so, the underlying device may get filled up in a
> > + * non-linear fashion. While that may not matter on non-rotational devices, for
> > + * rotational devices that may result in higher seek times. "mb_linear_limit"
> > + * tells mballoc how many groups mballoc should search linearly before
> > + * performing consulting above data structures for more efficient lookups. For
> > + * non rotational devices, this value defaults to 0 and for rotational devices
> > + * this is set to MB_DEFAULT_LINEAR_LIMIT.
> > + *
> > * Both the prealloc space are getting populated as above. So for the first
> > * request we will hit the buddy cache which will result in this prealloc
> > * space getting filled. The prealloc space is then later used for the
> > @@ -299,6 +348,8 @@
> > * - bitlock on a group (group)
> > * - object (inode/locality) (object)
> > * - per-pa lock (pa)
> > + * - cr0 lists lock (cr0)
> > + * - cr1 tree lock (cr1)
> > *
> > * Paths:
> > * - new pa
> > @@ -328,6 +379,9 @@
> > * group
> > * object
> > *
> > + * - allocation path (ext4_mb_regular_allocator)
> > + * group
> > + * cr0/cr1
> > */
> > static struct kmem_cache *ext4_pspace_cachep;
> > static struct kmem_cache *ext4_ac_cachep;
> > @@ -351,6 +405,9 @@ static void ext4_mb_generate_from_freelist(struct super_block *sb, void *bitmap,
> > ext4_group_t group);
> > static void ext4_mb_new_preallocation(struct ext4_allocation_context *ac);
> >
> > +static bool ext4_mb_good_group(struct ext4_allocation_context *ac,
> > + ext4_group_t group, int cr);
> > +
> > /*
> > * The algorithm using this percpu seq counter goes below:
> > * 1. We sample the percpu discard_pa_seq counter before trying for block
> > @@ -744,6 +801,251 @@ static void ext4_mb_mark_free_simple(struct super_block *sb,
> > }
> > }
> >
> > +static void ext4_mb_rb_insert(struct rb_root *root, struct rb_node *new,
> > + int (*cmp)(struct rb_node *, struct rb_node *))
> > +{
> > + struct rb_node **iter = &root->rb_node, *parent = NULL;
> > +
> > + while (*iter) {
> > + parent = *iter;
> > + if (cmp(new, *iter))
> > + iter = &((*iter)->rb_left);
> > + else
> > + iter = &((*iter)->rb_right);
> > + }
> > +
> > + rb_link_node(new, parent, iter);
> > + rb_insert_color(new, root);
> > +}
> > +
> > +static int
> > +ext4_mb_avg_fragment_size_cmp(struct rb_node *rb1, struct rb_node *rb2)
> > +{
> > + struct ext4_group_info *grp1 = rb_entry(rb1,
> > + struct ext4_group_info,
> > + bb_avg_fragment_size_rb);
> > + struct ext4_group_info *grp2 = rb_entry(rb2,
> > + struct ext4_group_info,
> > + bb_avg_fragment_size_rb);
> > + int num_frags_1, num_frags_2;
> > +
> > + num_frags_1 = grp1->bb_fragments ?
> > + grp1->bb_free / grp1->bb_fragments : 0;
> > + num_frags_2 = grp2->bb_fragments ?
> > + grp2->bb_free / grp2->bb_fragments : 0;
> > +
> > + return (num_frags_1 < num_frags_2);
> > +}
> > +
> > +/*
> > + * Reinsert grpinfo into the avg_fragment_size tree with new average
> > + * fragment size.
> > + */
> > +static void
> > +mb_update_avg_fragment_size(struct super_block *sb, struct ext4_group_info *grp)
> > +{
> > + struct ext4_sb_info *sbi = EXT4_SB(sb);
> > +
> > + if (!test_opt2(sb, MB_OPTIMIZE_SCAN) || grp->bb_free == 0)
> > + return;
> > +
> > + write_lock(&sbi->s_mb_rb_lock);
> > + if (!RB_EMPTY_NODE(&grp->bb_avg_fragment_size_rb)) {
> > + rb_erase(&grp->bb_avg_fragment_size_rb,
> > + &sbi->s_mb_avg_fragment_size_root);
> > + RB_CLEAR_NODE(&grp->bb_avg_fragment_size_rb);
> > + }
> > +
> > + ext4_mb_rb_insert(&sbi->s_mb_avg_fragment_size_root,
> > + &grp->bb_avg_fragment_size_rb,
> > + ext4_mb_avg_fragment_size_cmp);
> > + write_unlock(&sbi->s_mb_rb_lock);
> > +}
> > +
> > +/*
> > + * Choose next group by traversing largest_free_order lists. Return 0 if next
> > + * group was selected optimally. Return 1 if next group was not selected
> > + * optimally. Updates *new_cr if cr level needs an update.
> > + */
> > +static int ext4_mb_choose_next_group_cr0(struct ext4_allocation_context *ac,
> > + int *new_cr, ext4_group_t *group, ext4_group_t ngroups)
> > +{
> > + struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
> > + struct ext4_group_info *iter, *grp;
> > + int i;
> > +
> > + if (ac->ac_status == AC_STATUS_FOUND)
> > + return 1;
> > +
> > + if (unlikely(sbi->s_mb_stats && ac->ac_flags & EXT4_MB_CR0_OPTIMIZED))
> > + atomic_inc(&sbi->s_bal_cr0_bad_suggestions);
> > +
> > + grp = NULL;
> > + for (i = ac->ac_2order; i < MB_NUM_ORDERS(ac->ac_sb); i++) {
> > + if (list_empty(&sbi->s_mb_largest_free_orders[i]))
> > + continue;
> > + read_lock(&sbi->s_mb_largest_free_orders_locks[i]);
> > + if (list_empty(&sbi->s_mb_largest_free_orders[i])) {
> > + read_unlock(&sbi->s_mb_largest_free_orders_locks[i]);
> > + continue;
> > + }
> > + grp = NULL;
> > + list_for_each_entry(iter, &sbi->s_mb_largest_free_orders[i],
> > + bb_largest_free_order_node) {
> > + if (sbi->s_mb_stats)
> > + atomic64_inc(&sbi->s_bal_cX_groups_considered[0]);
> > + if (likely(ext4_mb_good_group(ac, iter->bb_group, 0))) {
> > + grp = iter;
> > + break;
> > + }
> > + }
> > + read_unlock(&sbi->s_mb_largest_free_orders_locks[i]);
> > + if (grp)
> > + break;
> > + }
> > +
> > + if (!grp) {
> > + /* Increment cr and search again */
> > + *new_cr = 1;
> > + } else {
> > + *group = grp->bb_group;
> > + ac->ac_last_optimal_group = *group;
> > + ac->ac_flags |= EXT4_MB_CR0_OPTIMIZED;
> > + }
> > + return 0;
> > +}
> > +
> > +/*
> > + * Choose next group by traversing average fragment size tree. Return 0 if next
> > + * group was selected optimally. Return 1 if next group could not selected
> > + * optimally (due to lock contention). Updates *new_cr if cr lvel needs an
> > + * update.
> > + */
> > +static int ext4_mb_choose_next_group_cr1(struct ext4_allocation_context *ac,
> > + int *new_cr, ext4_group_t *group, ext4_group_t ngroups)
> > +{
> > + struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
> > + int avg_fragment_size, best_so_far;
> > + struct rb_node *node, *found;
> > + struct ext4_group_info *grp;
> > +
> > + /*
> > + * If there is contention on the lock, instead of waiting for the lock
> > + * to become available, just continue searching lineraly. We'll resume
> > + * our rb tree search later starting at ac->ac_last_optimal_group.
> > + */
> > + if (!read_trylock(&sbi->s_mb_rb_lock))
> > + return 1;
> > +
> > + if (unlikely(ac->ac_flags & EXT4_MB_CR1_OPTIMIZED)) {
> > + if (sbi->s_mb_stats)
> > + atomic_inc(&sbi->s_bal_cr1_bad_suggestions);
> > + /* We have found something at CR 1 in the past */
> > + grp = ext4_get_group_info(ac->ac_sb, ac->ac_last_optimal_group);
> > + for (found = rb_next(&grp->bb_avg_fragment_size_rb); found != NULL;
> > + found = rb_next(found)) {
> > + grp = rb_entry(found, struct ext4_group_info,
> > + bb_avg_fragment_size_rb);
> > + if (sbi->s_mb_stats)
> > + atomic64_inc(&sbi->s_bal_cX_groups_considered[1]);
> > + if (likely(ext4_mb_good_group(ac, grp->bb_group, 1)))
> > + break;
> > + }
> > +
> > + goto done;
> > + }
> > +
> > + node = sbi->s_mb_avg_fragment_size_root.rb_node;
> > + best_so_far = 0;
> > + found = NULL;
> > +
> > + while (node) {
> > + grp = rb_entry(node, struct ext4_group_info,
> > + bb_avg_fragment_size_rb);
> > + avg_fragment_size = 0;
> > + /*
> > + * Perform this check without locking, we'll lock later to confirm.
> > + */
> > + if (ext4_mb_good_group(ac, grp->bb_group, 1)) {
> > + avg_fragment_size = grp->bb_fragments ?
> > + grp->bb_free / grp->bb_fragments : 0;
> > + if (!best_so_far || avg_fragment_size < best_so_far) {
> > + best_so_far = avg_fragment_size;
> > + found = node;
> > + }
> > + }
> > + if (avg_fragment_size > ac->ac_g_ex.fe_len)
> > + node = node->rb_right;
> > + else
> > + node = node->rb_left;
> > + }
> > +
> > +done:
> > + if (found) {
> > + grp = rb_entry(found, struct ext4_group_info,
> > + bb_avg_fragment_size_rb);
> > + *group = grp->bb_group;
> > + ac->ac_flags |= EXT4_MB_CR1_OPTIMIZED;
> > + } else {
> > + *new_cr = 2;
> > + }
> > +
> > + read_unlock(&sbi->s_mb_rb_lock);
> > + ac->ac_last_optimal_group = *group;
> > + return 0;
> > +}
> > +
> > +/*
> > + * ext4_mb_choose_next_group: choose next group for allocation.
> > + *
> > + * @ac Allocation Context
> > + * @new_cr This is an output parameter. If the there is no good group
> > + * available at current CR level, this field is updated to indicate
> > + * the new cr level that should be used.
> > + * @group This is an input / output parameter. As an input it indicates the
> > + * last group used for allocation. As output, this field indicates
> > + * the next group that should be used.
> > + * @ngroups Total number of groups
> > + */
> > +static void ext4_mb_choose_next_group(struct ext4_allocation_context *ac,
> > + int *new_cr, ext4_group_t *group, ext4_group_t ngroups)
> > +{
> > + int ret;
> > +
> > + *new_cr = ac->ac_criteria;
> > +
> > + if (!test_opt2(ac->ac_sb, MB_OPTIMIZE_SCAN) ||
> > + *new_cr >= 2 ||
> > + !ext4_test_inode_flag(ac->ac_inode, EXT4_INODE_EXTENTS))
> > + goto inc_and_return;
> > +
> > + if (ac->ac_groups_linear_remaining) {
> > + ac->ac_groups_linear_remaining--;
> > + goto inc_and_return;
> > + }
> > +
> > + if (*new_cr == 0) {
> > + ret = ext4_mb_choose_next_group_cr0(ac, new_cr, group, ngroups);
> > + if (ret)
> > + goto inc_and_return;
> > + }
> > + if (*new_cr == 1) {
> > + ret = ext4_mb_choose_next_group_cr1(ac, new_cr, group, ngroups);
> > + if (ret)
> > + goto inc_and_return;
> > + }
> > + return;
> > +
> > +inc_and_return:
> > + /*
> > + * Artificially restricted ngroups for non-extent
> > + * files makes group > ngroups possible on first loop.
> > + */
> > + *group = *group + 1;
> > + if (*group >= ngroups)
> > + *group = 0;
> > +}
> > +
> > /*
> > * Cache the order of the largest free extent we have available in this block
> > * group.
> > @@ -751,18 +1053,33 @@ static void ext4_mb_mark_free_simple(struct super_block *sb,
> > static void
> > mb_set_largest_free_order(struct super_block *sb, struct ext4_group_info *grp)
> > {
> > + struct ext4_sb_info *sbi = EXT4_SB(sb);
> > int i;
> > - int bits;
> >
> > + if (test_opt2(sb, MB_OPTIMIZE_SCAN) && grp->bb_largest_free_order >= 0) {
> > + write_lock(&sbi->s_mb_largest_free_orders_locks[
> > + grp->bb_largest_free_order]);
> > + list_del_init(&grp->bb_largest_free_order_node);
> > + write_unlock(&sbi->s_mb_largest_free_orders_locks[
> > + grp->bb_largest_free_order]);
> > + }
> > grp->bb_largest_free_order = -1; /* uninit */
> >
> > - bits = MB_NUM_ORDERS(sb) - 1;
> > - for (i = bits; i >= 0; i--) {
> > + for (i = MB_NUM_ORDERS(sb) - 1; i >= 0; i--) {
> > if (grp->bb_counters[i] > 0) {
> > grp->bb_largest_free_order = i;
> > break;
> > }
> > }
> > + if (test_opt2(sb, MB_OPTIMIZE_SCAN) &&
> > + grp->bb_largest_free_order >= 0 && grp->bb_free) {
> > + write_lock(&sbi->s_mb_largest_free_orders_locks[
> > + grp->bb_largest_free_order]);
> > + list_add_tail(&grp->bb_largest_free_order_node,
> > + &sbi->s_mb_largest_free_orders[grp->bb_largest_free_order]);
> > + write_unlock(&sbi->s_mb_largest_free_orders_locks[
> > + grp->bb_largest_free_order]);
> > + }
> > }
> >
> > static noinline_for_stack
> > @@ -818,6 +1135,7 @@ void ext4_mb_generate_buddy(struct super_block *sb,
> > period = get_cycles() - period;
> > atomic_inc(&sbi->s_mb_buddies_generated);
> > atomic64_add(period, &sbi->s_mb_generation_time);
> > + mb_update_avg_fragment_size(sb, grp);
> > }
> >
> > /* The buddy information is attached the buddy cache inode
> > @@ -1517,6 +1835,7 @@ static void mb_free_blocks(struct inode *inode, struct ext4_buddy *e4b,
> >
> > done:
> > mb_set_largest_free_order(sb, e4b->bd_info);
> > + mb_update_avg_fragment_size(sb, e4b->bd_info);
> > mb_check_buddy(e4b);
> > }
> >
> > @@ -1653,6 +1972,7 @@ static int mb_mark_used(struct ext4_buddy *e4b, struct ext4_free_extent *ex)
> > }
> > mb_set_largest_free_order(e4b->bd_sb, e4b->bd_info);
> >
> > + mb_update_avg_fragment_size(e4b->bd_sb, e4b->bd_info);
> > ext4_set_bits(e4b->bd_bitmap, ex->fe_start, len0);
> > mb_check_buddy(e4b);
> >
> > @@ -2347,17 +2667,21 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
> > * from the goal value specified
> > */
> > group = ac->ac_g_ex.fe_group;
> > + ac->ac_last_optimal_group = group;
> > + ac->ac_groups_linear_remaining = sbi->s_mb_linear_limit;
> > prefetch_grp = group;
> >
> > - for (i = 0; i < ngroups; group++, i++) {
> > - int ret = 0;
> > + for (i = 0; i < ngroups; i++) {
> > + int ret = 0, new_cr;
> > +
> > cond_resched();
> > - /*
> > - * Artificially restricted ngroups for non-extent
> > - * files makes group > ngroups possible on first loop.
> > - */
> > - if (group >= ngroups)
> > - group = 0;
> > +
> > + ext4_mb_choose_next_group(ac, &new_cr, &group, ngroups);
> > +
> > + if (new_cr != cr) {
> > + cr = new_cr;
> > + goto repeat;
> > + }
> >
> > /*
> > * Batch reads of the block allocation bitmaps
> > @@ -2578,6 +2902,8 @@ int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset)
> > atomic64_read(&sbi->s_bal_cX_groups_considered[0]));
> > seq_printf(seq, "\t\tuseless_loops: %llu\n",
> > atomic64_read(&sbi->s_bal_cX_failed[0]));
> > + seq_printf(seq, "\t\tbad_suggestions: %u\n",
> > + atomic_read(&sbi->s_bal_cr0_bad_suggestions));
> >
> > seq_puts(seq, "\tcr1_stats:\n");
> > seq_printf(seq, "\t\thits: %llu\n", atomic64_read(&sbi->s_bal_cX_hits[1]));
> > @@ -2585,6 +2911,8 @@ int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset)
> > atomic64_read(&sbi->s_bal_cX_groups_considered[1]));
> > seq_printf(seq, "\t\tuseless_loops: %llu\n",
> > atomic64_read(&sbi->s_bal_cX_failed[1]));
> > + seq_printf(seq, "\t\tbad_suggestions: %u\n",
> > + atomic_read(&sbi->s_bal_cr1_bad_suggestions));
> >
> > seq_puts(seq, "\tcr2_stats:\n");
> > seq_printf(seq, "\t\thits: %llu\n", atomic64_read(&sbi->s_bal_cX_hits[2]));
> > @@ -2719,7 +3047,10 @@ int ext4_mb_add_groupinfo(struct super_block *sb, ext4_group_t group,
> > INIT_LIST_HEAD(&meta_group_info[i]->bb_prealloc_list);
> > init_rwsem(&meta_group_info[i]->alloc_sem);
> > meta_group_info[i]->bb_free_root = RB_ROOT;
> > + INIT_LIST_HEAD(&meta_group_info[i]->bb_largest_free_order_node);
> > + RB_CLEAR_NODE(&meta_group_info[i]->bb_avg_fragment_size_rb);
> > meta_group_info[i]->bb_largest_free_order = -1; /* uninit */
> > + meta_group_info[i]->bb_group = group;
> >
> > mb_group_bb_bitmap_alloc(sb, meta_group_info[i], group);
> > return 0;
> > @@ -2909,6 +3240,22 @@ int ext4_mb_init(struct super_block *sb)
> > i++;
> > } while (i < MB_NUM_ORDERS(sb));
> >
> > + sbi->s_mb_avg_fragment_size_root = RB_ROOT;
> > + sbi->s_mb_largest_free_orders =
> > + kmalloc_array(MB_NUM_ORDERS(sb), sizeof(struct list_head),
> > + GFP_KERNEL);
> > + if (!sbi->s_mb_largest_free_orders)
> > + goto out;
> > + sbi->s_mb_largest_free_orders_locks =
> > + kmalloc_array(MB_NUM_ORDERS(sb), sizeof(rwlock_t),
> > + GFP_KERNEL);
> > + if (!sbi->s_mb_largest_free_orders_locks)
> > + goto out;
> > + for (i = 0; i < MB_NUM_ORDERS(sb); i++) {
> > + INIT_LIST_HEAD(&sbi->s_mb_largest_free_orders[i]);
> > + rwlock_init(&sbi->s_mb_largest_free_orders_locks[i]);
> > + }
> > + rwlock_init(&sbi->s_mb_rb_lock);
> >
> > spin_lock_init(&sbi->s_md_lock);
> > sbi->s_mb_free_pending = 0;
> > @@ -2961,6 +3308,10 @@ int ext4_mb_init(struct super_block *sb)
> > spin_lock_init(&lg->lg_prealloc_lock);
> > }
> >
> > + if (blk_queue_nonrot(bdev_get_queue(sb->s_bdev)))
> > + sbi->s_mb_linear_limit = 0;
> > + else
> > + sbi->s_mb_linear_limit = MB_DEFAULT_LINEAR_LIMIT;
> > /* init file for buddy data */
> > ret = ext4_mb_init_backend(sb);
> > if (ret != 0)
> > @@ -2972,6 +3323,8 @@ int ext4_mb_init(struct super_block *sb)
> > free_percpu(sbi->s_locality_groups);
> > sbi->s_locality_groups = NULL;
> > out:
> > + kfree(sbi->s_mb_largest_free_orders);
> > + kfree(sbi->s_mb_largest_free_orders_locks);
> > kfree(sbi->s_mb_offsets);
> > sbi->s_mb_offsets = NULL;
> > kfree(sbi->s_mb_maxs);
> > @@ -3028,6 +3381,7 @@ int ext4_mb_release(struct super_block *sb)
> > kvfree(group_info);
> > rcu_read_unlock();
> > }
> > + kfree(sbi->s_mb_largest_free_orders);
> > kfree(sbi->s_mb_offsets);
> > kfree(sbi->s_mb_maxs);
> > iput(sbi->s_buddy_cache);
> > diff --git a/fs/ext4/mballoc.h b/fs/ext4/mballoc.h
> > index 68111a10cfee..02585e3cbcad 100644
> > --- a/fs/ext4/mballoc.h
> > +++ b/fs/ext4/mballoc.h
> > @@ -78,6 +78,18 @@
> > */
> > #define MB_DEFAULT_MAX_INODE_PREALLOC 512
> >
> > +/*
> > + * Number of groups to search linearly before performing group scanning
> > + * optimization.
> > + */
> > +#define MB_DEFAULT_LINEAR_LIMIT 4
> > +
> > +/*
> > + * Minimum number of groups that should be present in the file system to perform
> > + * group scanning optimizations.
> > + */
> > +#define MB_DEFAULT_LINEAR_SCAN_THRESHOLD 16
> > +
> > /*
> > * Number of valid buddy orders
> > */
> > @@ -166,11 +178,14 @@ struct ext4_allocation_context {
> > /* copy of the best found extent taken before preallocation efforts */
> > struct ext4_free_extent ac_f_ex;
> >
> > + ext4_group_t ac_last_optimal_group;
> > + __u32 ac_groups_considered;
> > + __u32 ac_flags; /* allocation hints */
> > __u16 ac_groups_scanned;
> > + __u16 ac_groups_linear_remaining;
> > __u16 ac_found;
> > __u16 ac_tail;
> > __u16 ac_buddy;
> > - __u16 ac_flags; /* allocation hints */
> > __u8 ac_status;
> > __u8 ac_criteria;
> > __u8 ac_2order; /* if request is to allocate 2^N blocks and
> > diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> > index 0491e7a6b04c..5b973f037298 100644
> > --- a/fs/ext4/super.c
> > +++ b/fs/ext4/super.c
> > @@ -1687,7 +1687,7 @@ enum {
> > Opt_dioread_nolock, Opt_dioread_lock,
> > Opt_discard, Opt_nodiscard, Opt_init_itable, Opt_noinit_itable,
> > Opt_max_dir_size_kb, Opt_nojournal_checksum, Opt_nombcache,
> > - Opt_prefetch_block_bitmaps,
> > + Opt_prefetch_block_bitmaps, Opt_mb_optimize_scan,
> > #ifdef CONFIG_EXT4_DEBUG
> > Opt_fc_debug_max_replay, Opt_fc_debug_force
> > #endif
> > @@ -1788,6 +1788,7 @@ static const match_table_t tokens = {
> > {Opt_nombcache, "nombcache"},
> > {Opt_nombcache, "no_mbcache"}, /* for backward compatibility */
> > {Opt_prefetch_block_bitmaps, "prefetch_block_bitmaps"},
> > + {Opt_mb_optimize_scan, "mb_optimize_scan=%d"},
> > {Opt_removed, "check=none"}, /* mount option from ext2/3 */
> > {Opt_removed, "nocheck"}, /* mount option from ext2/3 */
> > {Opt_removed, "reservation"}, /* mount option from ext2/3 */
> > @@ -1820,6 +1821,8 @@ static ext4_fsblk_t get_sb_block(void **data)
> > }
> >
> > #define DEFAULT_JOURNAL_IOPRIO (IOPRIO_PRIO_VALUE(IOPRIO_CLASS_BE, 3))
> > +#define DEFAULT_MB_OPTIMIZE_SCAN (-1)
> > +
> > static const char deprecated_msg[] =
> > "Mount option \"%s\" will be removed by %s\n"
> > "Contact [email protected] if you think we should keep it.\n";
> > @@ -2008,6 +2011,7 @@ static const struct mount_opts {
> > {Opt_nombcache, EXT4_MOUNT_NO_MBCACHE, MOPT_SET},
> > {Opt_prefetch_block_bitmaps, EXT4_MOUNT_PREFETCH_BLOCK_BITMAPS,
> > MOPT_SET},
> > + {Opt_mb_optimize_scan, EXT4_MOUNT2_MB_OPTIMIZE_SCAN, MOPT_GTE0},
> > #ifdef CONFIG_EXT4_DEBUG
> > {Opt_fc_debug_force, EXT4_MOUNT2_JOURNAL_FAST_COMMIT,
> > MOPT_SET | MOPT_2 | MOPT_EXT4_ONLY},
> > @@ -2092,6 +2096,7 @@ static int ext4_set_test_dummy_encryption(struct super_block *sb,
> > struct ext4_parsed_options {
> > unsigned long journal_devnum;
> > unsigned int journal_ioprio;
> > + int mb_optimize_scan;
> > };
> >
> > static int handle_mount_opt(struct super_block *sb, char *opt, int token,
> > @@ -2388,6 +2393,13 @@ static int handle_mount_opt(struct super_block *sb, char *opt, int token,
> > sbi->s_mount_opt |= m->mount_opt;
> > } else if (token == Opt_data_err_ignore) {
> > sbi->s_mount_opt &= ~m->mount_opt;
> > + } else if (token == Opt_mb_optimize_scan) {
> > + if (arg != 0 && arg != 1) {
> > + ext4_msg(sb, KERN_WARNING,
> > + "mb_optimize_scan should be set to 0 or 1.");
> > + return -1;
> > + }
> > + parsed_opts->mb_optimize_scan = arg;
> > } else {
> > if (!args->from)
> > arg = 1;
> > @@ -4034,6 +4046,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> > /* Set defaults for the variables that will be set during parsing */
> > parsed_opts.journal_ioprio = DEFAULT_JOURNAL_IOPRIO;
> > parsed_opts.journal_devnum = 0;
> > + parsed_opts.mb_optimize_scan = DEFAULT_MB_OPTIMIZE_SCAN;
> >
> > if ((data && !orig_data) || !sbi)
> > goto out_free_base;
> > @@ -4984,6 +4997,19 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> > ext4_fc_replay_cleanup(sb);
> >
> > ext4_ext_init(sb);
> > +
> > + /*
> > + * Enable optimize_scan if number of groups is > threshold. This can be
> > + * turned off by passing "mb_optimize_scan=0". This can also be
> > + * turned on forcefully by passing "mb_optimize_scan=1".
> > + */
> > + if (parsed_opts.mb_optimize_scan == 1)
> > + set_opt2(sb, MB_OPTIMIZE_SCAN);
> > + else if (parsed_opts.mb_optimize_scan == 0)
> > + clear_opt2(sb, MB_OPTIMIZE_SCAN);
> > + else if (sbi->s_groups_count >= MB_DEFAULT_LINEAR_SCAN_THRESHOLD)
> > + set_opt2(sb, MB_OPTIMIZE_SCAN);
> > +
> > err = ext4_mb_init(sb);
> > if (err) {
> > ext4_msg(sb, KERN_ERR, "failed to initialize mballoc (%d)",
> > diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c
> > index 59ca9d73b42f..16b8a838f631 100644
> > --- a/fs/ext4/sysfs.c
> > +++ b/fs/ext4/sysfs.c
> > @@ -213,6 +213,7 @@ EXT4_RW_ATTR_SBI_UI(mb_order2_req, s_mb_order2_reqs);
> > EXT4_RW_ATTR_SBI_UI(mb_stream_req, s_mb_stream_request);
> > EXT4_RW_ATTR_SBI_UI(mb_group_prealloc, s_mb_group_prealloc);
> > EXT4_RW_ATTR_SBI_UI(mb_max_inode_prealloc, s_mb_max_inode_prealloc);
> > +EXT4_RW_ATTR_SBI_UI(mb_linear_limit, s_mb_linear_limit);
> > EXT4_RW_ATTR_SBI_UI(extent_max_zeroout_kb, s_extent_max_zeroout_kb);
> > EXT4_ATTR(trigger_fs_error, 0200, trigger_test_error);
> > EXT4_RW_ATTR_SBI_UI(err_ratelimit_interval_ms, s_err_ratelimit_state.interval);
> > @@ -260,6 +261,7 @@ static struct attribute *ext4_attrs[] = {
> > ATTR_LIST(mb_stream_req),
> > ATTR_LIST(mb_group_prealloc),
> > ATTR_LIST(mb_max_inode_prealloc),
> > + ATTR_LIST(mb_linear_limit),
> > ATTR_LIST(max_writeback_mb_bump),
> > ATTR_LIST(extent_max_zeroout_kb),
> > ATTR_LIST(trigger_fs_error),
> > --
> > 2.31.0.rc2.261.g7f71774620-goog
> >
>