Changelog:
v7:
* Added the mem_cgroup_iter_online() function to the API for the new
behavior (suggested by Andrew Morton) (patch 2)
* Fixed a missing list_lru_del -> list_lru_del_obj (patch 1)
v6:
* Rebase on top of latest mm-unstable.
* Fix/improve the in-code documentation of the new list_lru
manipulation functions (patch 1)
v5:
* Replace reference getting with an rcu_read_lock() section for
zswap lru modifications (suggested by Yosry)
* Add a new prep patch that allows mem_cgroup_iter() to return
online cgroup.
* Add a callback that updates pool->next_shrink when the cgroup is
offlined (suggested by Yosry Ahmed, Johannes Weiner)
v4:
* Rename list_lru_add to list_lru_add_obj and __list_lru_add to
list_lru_add (patch 1) (suggested by Johannes Weiner and
Yosry Ahmed)
* Some cleanups on the memcg aware LRU patch (patch 2)
(suggested by Yosry Ahmed)
* Use event interface for the new per-cgroup writeback counters.
(patch 3) (suggested by Yosry Ahmed)
* Abstract zswap's lruvec states and handling into
zswap_lruvec_state (patch 5) (suggested by Yosry Ahmed)
v3:
* Add a patch to export per-cgroup zswap writeback counters
* Add a patch to update zswap's kselftest
* Separate the new list_lru functions into its own prep patch
* Do not start from the top of the hierarchy when encounter a memcg
that is not online for the global limit zswap writeback (patch 2)
(suggested by Yosry Ahmed)
* Do not remove the swap entry from list_lru in
__read_swapcache_async() (patch 2) (suggested by Yosry Ahmed)
* Removed a redundant zswap pool getting (patch 2)
(reported by Ryan Roberts)
* Use atomic for the nr_zswap_protected (instead of lruvec's lock)
(patch 5) (suggested by Yosry Ahmed)
* Remove the per-cgroup zswap shrinker knob (patch 5)
(suggested by Yosry Ahmed)
v2:
* Fix loongarch compiler errors
* Use pool stats instead of memcg stats when !CONFIG_MEMCG_KEM
There are currently several issues with zswap writeback:
1. There is only a single global LRU for zswap, making it impossible to
perform worload-specific shrinking - an memcg under memory pressure
cannot determine which pages in the pool it owns, and often ends up
writing pages from other memcgs. This issue has been previously
observed in practice and mitigated by simply disabling
memcg-initiated shrinking:
https://lore.kernel.org/all/[email protected]/T/#u
But this solution leaves a lot to be desired, as we still do not
have an avenue for an memcg to free up its own memory locked up in
the zswap pool.
2. We only shrink the zswap pool when the user-defined limit is hit.
This means that if we set the limit too high, cold data that are
unlikely to be used again will reside in the pool, wasting precious
memory. It is hard to predict how much zswap space will be needed
ahead of time, as this depends on the workload (specifically, on
factors such as memory access patterns and compressibility of the
memory pages).
This patch series solves these issues by separating the global zswap
LRU into per-memcg and per-NUMA LRUs, and performs workload-specific
(i.e memcg- and NUMA-aware) zswap writeback under memory pressure. The
new shrinker does not have any parameter that must be tuned by the
user, and can be opted in or out on a per-memcg basis.
As a proof of concept, we ran the following synthetic benchmark:
build the linux kernel in a memory-limited cgroup, and allocate some
cold data in tmpfs to see if the shrinker could write them out and
improved the overall performance. Depending on the amount of cold data
generated, we observe from 14% to 35% reduction in kernel CPU time used
in the kernel builds.
Domenico Cerasuolo (3):
zswap: make shrinking memcg-aware
mm: memcg: add per-memcg zswap writeback stat
selftests: cgroup: update per-memcg zswap writeback selftest
Nhat Pham (3):
list_lru: allows explicit memcg and NUMA node selection
memcontrol: add a new function to traverse online-only memcg hierarchy
zswap: shrinks zswap pool based on memory pressure
Documentation/admin-guide/mm/zswap.rst | 7 +
drivers/android/binder_alloc.c | 7 +-
fs/dcache.c | 8 +-
fs/gfs2/quota.c | 6 +-
fs/inode.c | 4 +-
fs/nfs/nfs42xattr.c | 8 +-
fs/nfsd/filecache.c | 4 +-
fs/xfs/xfs_buf.c | 6 +-
fs/xfs/xfs_dquot.c | 2 +-
fs/xfs/xfs_qm.c | 2 +-
include/linux/list_lru.h | 54 ++-
include/linux/memcontrol.h | 18 +
include/linux/mmzone.h | 2 +
include/linux/vm_event_item.h | 1 +
include/linux/zswap.h | 27 +-
mm/list_lru.c | 48 ++-
mm/memcontrol.c | 32 +-
mm/mmzone.c | 1 +
mm/swap.h | 3 +-
mm/swap_state.c | 26 +-
mm/vmstat.c | 1 +
mm/workingset.c | 4 +-
mm/zswap.c | 426 +++++++++++++++++---
tools/testing/selftests/cgroup/test_zswap.c | 74 ++--
24 files changed, 641 insertions(+), 130 deletions(-)
base-commit: 5cdba94229e58a39ca389ad99763af29e6b0c5a5
--
2.34.1
The interface of list_lru is based on the assumption that the list node
and the data it represents belong to the same allocated on the correct
node/memcg. While this assumption is valid for existing slab objects LRU
such as dentries and inodes, it is undocumented, and rather inflexible
for certain potential list_lru users (such as the upcoming zswap
shrinker and the THP shrinker). It has caused us a lot of issues during
our development.
This patch changes list_lru interface so that the caller must explicitly
specify numa node and memcg when adding and removing objects. The old
list_lru_add() and list_lru_del() are renamed to list_lru_add_obj() and
list_lru_del_obj(), respectively.
It also extends the list_lru API with a new function, list_lru_putback,
which undoes a previous list_lru_isolate call. Unlike list_lru_add, it
does not increment the LRU node count (as list_lru_isolate does not
decrement the node count). list_lru_putback also allows for explicit
memcg and NUMA node selection.
Suggested-by: Johannes Weiner <[email protected]>
Signed-off-by: Nhat Pham <[email protected]>
---
drivers/android/binder_alloc.c | 7 ++---
fs/dcache.c | 8 +++--
fs/gfs2/quota.c | 6 ++--
fs/inode.c | 4 +--
fs/nfs/nfs42xattr.c | 8 ++---
fs/nfsd/filecache.c | 4 +--
fs/xfs/xfs_buf.c | 6 ++--
fs/xfs/xfs_dquot.c | 2 +-
fs/xfs/xfs_qm.c | 2 +-
include/linux/list_lru.h | 54 ++++++++++++++++++++++++++++++++--
mm/list_lru.c | 48 +++++++++++++++++++++++++-----
mm/workingset.c | 4 +--
12 files changed, 117 insertions(+), 36 deletions(-)
diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index 138f6d43d13b..f69d30c9f50f 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -234,7 +234,7 @@ static int binder_update_page_range(struct binder_alloc *alloc, int allocate,
if (page->page_ptr) {
trace_binder_alloc_lru_start(alloc, index);
- on_lru = list_lru_del(&binder_alloc_lru, &page->lru);
+ on_lru = list_lru_del_obj(&binder_alloc_lru, &page->lru);
WARN_ON(!on_lru);
trace_binder_alloc_lru_end(alloc, index);
@@ -285,7 +285,7 @@ static int binder_update_page_range(struct binder_alloc *alloc, int allocate,
trace_binder_free_lru_start(alloc, index);
- ret = list_lru_add(&binder_alloc_lru, &page->lru);
+ ret = list_lru_add_obj(&binder_alloc_lru, &page->lru);
WARN_ON(!ret);
trace_binder_free_lru_end(alloc, index);
@@ -848,7 +848,7 @@ void binder_alloc_deferred_release(struct binder_alloc *alloc)
if (!alloc->pages[i].page_ptr)
continue;
- on_lru = list_lru_del(&binder_alloc_lru,
+ on_lru = list_lru_del_obj(&binder_alloc_lru,
&alloc->pages[i].lru);
page_addr = alloc->buffer + i * PAGE_SIZE;
binder_alloc_debug(BINDER_DEBUG_BUFFER_ALLOC,
@@ -1287,4 +1287,3 @@ int binder_alloc_copy_from_buffer(struct binder_alloc *alloc,
return binder_alloc_do_buffer_copy(alloc, false, buffer, buffer_offset,
dest, bytes);
}
-
diff --git a/fs/dcache.c b/fs/dcache.c
index c82ae731df9a..2ba37643b9c5 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -428,7 +428,8 @@ static void d_lru_add(struct dentry *dentry)
this_cpu_inc(nr_dentry_unused);
if (d_is_negative(dentry))
this_cpu_inc(nr_dentry_negative);
- WARN_ON_ONCE(!list_lru_add(&dentry->d_sb->s_dentry_lru, &dentry->d_lru));
+ WARN_ON_ONCE(!list_lru_add_obj(
+ &dentry->d_sb->s_dentry_lru, &dentry->d_lru));
}
static void d_lru_del(struct dentry *dentry)
@@ -438,7 +439,8 @@ static void d_lru_del(struct dentry *dentry)
this_cpu_dec(nr_dentry_unused);
if (d_is_negative(dentry))
this_cpu_dec(nr_dentry_negative);
- WARN_ON_ONCE(!list_lru_del(&dentry->d_sb->s_dentry_lru, &dentry->d_lru));
+ WARN_ON_ONCE(!list_lru_del_obj(
+ &dentry->d_sb->s_dentry_lru, &dentry->d_lru));
}
static void d_shrink_del(struct dentry *dentry)
@@ -1240,7 +1242,7 @@ static enum lru_status dentry_lru_isolate(struct list_head *item,
*
* This is guaranteed by the fact that all LRU management
* functions are intermediated by the LRU API calls like
- * list_lru_add and list_lru_del. List movement in this file
+ * list_lru_add_obj and list_lru_del_obj. List movement in this file
* only ever occur through this functions or through callbacks
* like this one, that are called from the LRU API.
*
diff --git a/fs/gfs2/quota.c b/fs/gfs2/quota.c
index 95dae7838b4e..b57f8c7b35be 100644
--- a/fs/gfs2/quota.c
+++ b/fs/gfs2/quota.c
@@ -271,7 +271,7 @@ static struct gfs2_quota_data *gfs2_qd_search_bucket(unsigned int hash,
if (qd->qd_sbd != sdp)
continue;
if (lockref_get_not_dead(&qd->qd_lockref)) {
- list_lru_del(&gfs2_qd_lru, &qd->qd_lru);
+ list_lru_del_obj(&gfs2_qd_lru, &qd->qd_lru);
return qd;
}
}
@@ -344,7 +344,7 @@ static void qd_put(struct gfs2_quota_data *qd)
}
qd->qd_lockref.count = 0;
- list_lru_add(&gfs2_qd_lru, &qd->qd_lru);
+ list_lru_add_obj(&gfs2_qd_lru, &qd->qd_lru);
spin_unlock(&qd->qd_lockref.lock);
}
@@ -1517,7 +1517,7 @@ void gfs2_quota_cleanup(struct gfs2_sbd *sdp)
lockref_mark_dead(&qd->qd_lockref);
spin_unlock(&qd->qd_lockref.lock);
- list_lru_del(&gfs2_qd_lru, &qd->qd_lru);
+ list_lru_del_obj(&gfs2_qd_lru, &qd->qd_lru);
list_add(&qd->qd_lru, &dispose);
}
spin_unlock(&qd_lock);
diff --git a/fs/inode.c b/fs/inode.c
index f238d987dec9..ef2034a985e0 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -464,7 +464,7 @@ static void __inode_add_lru(struct inode *inode, bool rotate)
if (!mapping_shrinkable(&inode->i_data))
return;
- if (list_lru_add(&inode->i_sb->s_inode_lru, &inode->i_lru))
+ if (list_lru_add_obj(&inode->i_sb->s_inode_lru, &inode->i_lru))
this_cpu_inc(nr_unused);
else if (rotate)
inode->i_state |= I_REFERENCED;
@@ -482,7 +482,7 @@ void inode_add_lru(struct inode *inode)
static void inode_lru_list_del(struct inode *inode)
{
- if (list_lru_del(&inode->i_sb->s_inode_lru, &inode->i_lru))
+ if (list_lru_del_obj(&inode->i_sb->s_inode_lru, &inode->i_lru))
this_cpu_dec(nr_unused);
}
diff --git a/fs/nfs/nfs42xattr.c b/fs/nfs/nfs42xattr.c
index 2ad66a8922f4..49aaf28a6950 100644
--- a/fs/nfs/nfs42xattr.c
+++ b/fs/nfs/nfs42xattr.c
@@ -132,7 +132,7 @@ nfs4_xattr_entry_lru_add(struct nfs4_xattr_entry *entry)
lru = (entry->flags & NFS4_XATTR_ENTRY_EXTVAL) ?
&nfs4_xattr_large_entry_lru : &nfs4_xattr_entry_lru;
- return list_lru_add(lru, &entry->lru);
+ return list_lru_add_obj(lru, &entry->lru);
}
static bool
@@ -143,7 +143,7 @@ nfs4_xattr_entry_lru_del(struct nfs4_xattr_entry *entry)
lru = (entry->flags & NFS4_XATTR_ENTRY_EXTVAL) ?
&nfs4_xattr_large_entry_lru : &nfs4_xattr_entry_lru;
- return list_lru_del(lru, &entry->lru);
+ return list_lru_del_obj(lru, &entry->lru);
}
/*
@@ -349,7 +349,7 @@ nfs4_xattr_cache_unlink(struct inode *inode)
oldcache = nfsi->xattr_cache;
if (oldcache != NULL) {
- list_lru_del(&nfs4_xattr_cache_lru, &oldcache->lru);
+ list_lru_del_obj(&nfs4_xattr_cache_lru, &oldcache->lru);
oldcache->inode = NULL;
}
nfsi->xattr_cache = NULL;
@@ -474,7 +474,7 @@ nfs4_xattr_get_cache(struct inode *inode, int add)
kref_get(&cache->ref);
nfsi->xattr_cache = cache;
cache->inode = inode;
- list_lru_add(&nfs4_xattr_cache_lru, &cache->lru);
+ list_lru_add_obj(&nfs4_xattr_cache_lru, &cache->lru);
}
spin_unlock(&inode->i_lock);
diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
index ef063f93fde9..6c2decfdeb4b 100644
--- a/fs/nfsd/filecache.c
+++ b/fs/nfsd/filecache.c
@@ -322,7 +322,7 @@ nfsd_file_check_writeback(struct nfsd_file *nf)
static bool nfsd_file_lru_add(struct nfsd_file *nf)
{
set_bit(NFSD_FILE_REFERENCED, &nf->nf_flags);
- if (list_lru_add(&nfsd_file_lru, &nf->nf_lru)) {
+ if (list_lru_add_obj(&nfsd_file_lru, &nf->nf_lru)) {
trace_nfsd_file_lru_add(nf);
return true;
}
@@ -331,7 +331,7 @@ static bool nfsd_file_lru_add(struct nfsd_file *nf)
static bool nfsd_file_lru_remove(struct nfsd_file *nf)
{
- if (list_lru_del(&nfsd_file_lru, &nf->nf_lru)) {
+ if (list_lru_del_obj(&nfsd_file_lru, &nf->nf_lru)) {
trace_nfsd_file_lru_del(nf);
return true;
}
diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 545c7991b9b5..669332849680 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -169,7 +169,7 @@ xfs_buf_stale(
atomic_set(&bp->b_lru_ref, 0);
if (!(bp->b_state & XFS_BSTATE_DISPOSE) &&
- (list_lru_del(&bp->b_target->bt_lru, &bp->b_lru)))
+ (list_lru_del_obj(&bp->b_target->bt_lru, &bp->b_lru)))
atomic_dec(&bp->b_hold);
ASSERT(atomic_read(&bp->b_hold) >= 1);
@@ -1047,7 +1047,7 @@ xfs_buf_rele(
* buffer for the LRU and clear the (now stale) dispose list
* state flag
*/
- if (list_lru_add(&bp->b_target->bt_lru, &bp->b_lru)) {
+ if (list_lru_add_obj(&bp->b_target->bt_lru, &bp->b_lru)) {
bp->b_state &= ~XFS_BSTATE_DISPOSE;
atomic_inc(&bp->b_hold);
}
@@ -1060,7 +1060,7 @@ xfs_buf_rele(
* was on was the disposal list
*/
if (!(bp->b_state & XFS_BSTATE_DISPOSE)) {
- list_lru_del(&bp->b_target->bt_lru, &bp->b_lru);
+ list_lru_del_obj(&bp->b_target->bt_lru, &bp->b_lru);
} else {
ASSERT(list_empty(&bp->b_lru));
}
diff --git a/fs/xfs/xfs_dquot.c b/fs/xfs/xfs_dquot.c
index ac6ba646624d..49f619f5aa96 100644
--- a/fs/xfs/xfs_dquot.c
+++ b/fs/xfs/xfs_dquot.c
@@ -1064,7 +1064,7 @@ xfs_qm_dqput(
struct xfs_quotainfo *qi = dqp->q_mount->m_quotainfo;
trace_xfs_dqput_free(dqp);
- if (list_lru_add(&qi->qi_lru, &dqp->q_lru))
+ if (list_lru_add_obj(&qi->qi_lru, &dqp->q_lru))
XFS_STATS_INC(dqp->q_mount, xs_qm_dquot_unused);
}
xfs_dqunlock(dqp);
diff --git a/fs/xfs/xfs_qm.c b/fs/xfs/xfs_qm.c
index 94a7932ac570..67d0a8564ff3 100644
--- a/fs/xfs/xfs_qm.c
+++ b/fs/xfs/xfs_qm.c
@@ -171,7 +171,7 @@ xfs_qm_dqpurge(
* hits zero, so it really should be on the freelist here.
*/
ASSERT(!list_empty(&dqp->q_lru));
- list_lru_del(&qi->qi_lru, &dqp->q_lru);
+ list_lru_del_obj(&qi->qi_lru, &dqp->q_lru);
XFS_STATS_DEC(dqp->q_mount, xs_qm_dquot_unused);
xfs_qm_dqdestroy(dqp);
diff --git a/include/linux/list_lru.h b/include/linux/list_lru.h
index db86ad78d428..7675a48a0701 100644
--- a/include/linux/list_lru.h
+++ b/include/linux/list_lru.h
@@ -75,6 +75,8 @@ void memcg_reparent_list_lrus(struct mem_cgroup *memcg, struct mem_cgroup *paren
* list_lru_add: add an element to the lru list's tail
* @lru: the lru pointer
* @item: the item to be added.
+ * @nid: the node id of the sublist to add the item to.
+ * @memcg: the cgroup of the sublist to add the item to.
*
* If the element is already part of a list, this function returns doing
* nothing. Therefore the caller does not need to keep state about whether or
@@ -87,12 +89,28 @@ void memcg_reparent_list_lrus(struct mem_cgroup *memcg, struct mem_cgroup *paren
*
* Return: true if the list was updated, false otherwise
*/
-bool list_lru_add(struct list_lru *lru, struct list_head *item);
+bool list_lru_add(struct list_lru *lru, struct list_head *item, int nid,
+ struct mem_cgroup *memcg);
/**
- * list_lru_del: delete an element to the lru list
+ * list_lru_add_obj: add an element to the lru list's tail
+ * @lru: the lru pointer
+ * @item: the item to be added.
+ *
+ * This function is similar to list_lru_add(), but the NUMA node and the
+ * memcg of the sublist is determined by @item list_head. This assumption is
+ * valid for slab objects LRU such as dentries, inodes, etc.
+ *
+ * Return value: true if the list was updated, false otherwise
+ */
+bool list_lru_add_obj(struct list_lru *lru, struct list_head *item);
+
+/**
+ * list_lru_del: delete an element from the lru list
* @lru: the lru pointer
* @item: the item to be deleted.
+ * @nid: the node id of the sublist to delete the item from.
+ * @memcg: the cgroup of the sublist to delete the item from.
*
* This function works analogously as list_lru_add() in terms of list
* manipulation. The comments about an element already pertaining to
@@ -100,7 +118,21 @@ bool list_lru_add(struct list_lru *lru, struct list_head *item);
*
* Return: true if the list was updated, false otherwise
*/
-bool list_lru_del(struct list_lru *lru, struct list_head *item);
+bool list_lru_del(struct list_lru *lru, struct list_head *item, int nid,
+ struct mem_cgroup *memcg);
+
+/**
+ * list_lru_del_obj: delete an element from the lru list
+ * @lru: the lru pointer
+ * @item: the item to be deleted.
+ *
+ * This function is similar to list_lru_del(), but the NUMA node and the
+ * memcg of the sublist is determined by @item list_head. This assumption is
+ * valid for slab objects LRU such as dentries, inodes, etc.
+ *
+ * Return value: true if the list was updated, false otherwise.
+ */
+bool list_lru_del_obj(struct list_lru *lru, struct list_head *item);
/**
* list_lru_count_one: return the number of objects currently held by @lru
@@ -138,6 +170,22 @@ static inline unsigned long list_lru_count(struct list_lru *lru)
void list_lru_isolate(struct list_lru_one *list, struct list_head *item);
void list_lru_isolate_move(struct list_lru_one *list, struct list_head *item,
struct list_head *head);
+/**
+ * list_lru_putback: undo list_lru_isolate
+ * @lru: the lru pointer.
+ * @item: the item to put back.
+ * @nid: the node id of the sublist to put the item back to.
+ * @memcg: the cgroup of the sublist to put the item back to.
+ *
+ * Put back an isolated item into its original LRU. Note that unlike
+ * list_lru_add, this does not increment the node LRU count (as
+ * list_lru_isolate does not originally decrement this count).
+ *
+ * Since we might have dropped the LRU lock in between, recompute list_lru_one
+ * from the node's id and memcg.
+ */
+void list_lru_putback(struct list_lru *lru, struct list_head *item, int nid,
+ struct mem_cgroup *memcg);
typedef enum lru_status (*list_lru_walk_cb)(struct list_head *item,
struct list_lru_one *list, spinlock_t *lock, void *cb_arg);
diff --git a/mm/list_lru.c b/mm/list_lru.c
index a05e5bef3b40..fcca67ac26ec 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -116,21 +116,19 @@ list_lru_from_kmem(struct list_lru *lru, int nid, void *ptr,
}
#endif /* CONFIG_MEMCG_KMEM */
-bool list_lru_add(struct list_lru *lru, struct list_head *item)
+bool list_lru_add(struct list_lru *lru, struct list_head *item, int nid,
+ struct mem_cgroup *memcg)
{
- int nid = page_to_nid(virt_to_page(item));
struct list_lru_node *nlru = &lru->node[nid];
- struct mem_cgroup *memcg;
struct list_lru_one *l;
spin_lock(&nlru->lock);
if (list_empty(item)) {
- l = list_lru_from_kmem(lru, nid, item, &memcg);
+ l = list_lru_from_memcg_idx(lru, nid, memcg_kmem_id(memcg));
list_add_tail(item, &l->list);
/* Set shrinker bit if the first element was added */
if (!l->nr_items++)
- set_shrinker_bit(memcg, nid,
- lru_shrinker_id(lru));
+ set_shrinker_bit(memcg, nid, lru_shrinker_id(lru));
nlru->nr_items++;
spin_unlock(&nlru->lock);
return true;
@@ -140,15 +138,25 @@ bool list_lru_add(struct list_lru *lru, struct list_head *item)
}
EXPORT_SYMBOL_GPL(list_lru_add);
-bool list_lru_del(struct list_lru *lru, struct list_head *item)
+bool list_lru_add_obj(struct list_lru *lru, struct list_head *item)
{
int nid = page_to_nid(virt_to_page(item));
+ struct mem_cgroup *memcg = list_lru_memcg_aware(lru) ?
+ mem_cgroup_from_slab_obj(item) : NULL;
+
+ return list_lru_add(lru, item, nid, memcg);
+}
+EXPORT_SYMBOL_GPL(list_lru_add_obj);
+
+bool list_lru_del(struct list_lru *lru, struct list_head *item, int nid,
+ struct mem_cgroup *memcg)
+{
struct list_lru_node *nlru = &lru->node[nid];
struct list_lru_one *l;
spin_lock(&nlru->lock);
if (!list_empty(item)) {
- l = list_lru_from_kmem(lru, nid, item, NULL);
+ l = list_lru_from_memcg_idx(lru, nid, memcg_kmem_id(memcg));
list_del_init(item);
l->nr_items--;
nlru->nr_items--;
@@ -160,6 +168,16 @@ bool list_lru_del(struct list_lru *lru, struct list_head *item)
}
EXPORT_SYMBOL_GPL(list_lru_del);
+bool list_lru_del_obj(struct list_lru *lru, struct list_head *item)
+{
+ int nid = page_to_nid(virt_to_page(item));
+ struct mem_cgroup *memcg = list_lru_memcg_aware(lru) ?
+ mem_cgroup_from_slab_obj(item) : NULL;
+
+ return list_lru_del(lru, item, nid, memcg);
+}
+EXPORT_SYMBOL_GPL(list_lru_del_obj);
+
void list_lru_isolate(struct list_lru_one *list, struct list_head *item)
{
list_del_init(item);
@@ -175,6 +193,20 @@ void list_lru_isolate_move(struct list_lru_one *list, struct list_head *item,
}
EXPORT_SYMBOL_GPL(list_lru_isolate_move);
+void list_lru_putback(struct list_lru *lru, struct list_head *item, int nid,
+ struct mem_cgroup *memcg)
+{
+ struct list_lru_one *list =
+ list_lru_from_memcg_idx(lru, nid, memcg_kmem_id(memcg));
+
+ if (list_empty(item)) {
+ list_add_tail(item, &list->list);
+ if (!list->nr_items++)
+ set_shrinker_bit(memcg, nid, lru_shrinker_id(lru));
+ }
+}
+EXPORT_SYMBOL_GPL(list_lru_putback);
+
unsigned long list_lru_count_one(struct list_lru *lru,
int nid, struct mem_cgroup *memcg)
{
diff --git a/mm/workingset.c b/mm/workingset.c
index b192e44a0e7c..c17d45c6f29b 100644
--- a/mm/workingset.c
+++ b/mm/workingset.c
@@ -615,12 +615,12 @@ void workingset_update_node(struct xa_node *node)
if (node->count && node->count == node->nr_values) {
if (list_empty(&node->private_list)) {
- list_lru_add(&shadow_nodes, &node->private_list);
+ list_lru_add_obj(&shadow_nodes, &node->private_list);
__inc_lruvec_kmem_state(node, WORKINGSET_NODES);
}
} else {
if (!list_empty(&node->private_list)) {
- list_lru_del(&shadow_nodes, &node->private_list);
+ list_lru_del_obj(&shadow_nodes, &node->private_list);
__dec_lruvec_kmem_state(node, WORKINGSET_NODES);
}
}
--
2.34.1
The new zswap writeback scheme requires an online-only memcg hierarchy
traversal. Add this functionality via the new mem_cgroup_iter_online()
function - the old mem_cgroup_iter() is a special case of this new
function.
Suggested-by: Andrew Morton <[email protected]>
Signed-off-by: Nhat Pham <[email protected]>
---
include/linux/memcontrol.h | 13 +++++++++++++
mm/memcontrol.c | 29 +++++++++++++++++++++++++----
2 files changed, 38 insertions(+), 4 deletions(-)
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 7bdcf3020d7a..5bfe41840e80 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -833,6 +833,10 @@ static inline void mem_cgroup_put(struct mem_cgroup *memcg)
struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *,
struct mem_cgroup *,
struct mem_cgroup_reclaim_cookie *);
+struct mem_cgroup *mem_cgroup_iter_online(struct mem_cgroup *root,
+ struct mem_cgroup *prev,
+ struct mem_cgroup_reclaim_cookie *reclaim,
+ bool online);
void mem_cgroup_iter_break(struct mem_cgroup *, struct mem_cgroup *);
void mem_cgroup_scan_tasks(struct mem_cgroup *memcg,
int (*)(struct task_struct *, void *), void *arg);
@@ -1386,6 +1390,15 @@ mem_cgroup_iter(struct mem_cgroup *root,
return NULL;
}
+static inline struct mem_cgroup *
+mem_cgroup_iter_online(struct mem_cgroup *root,
+ struct mem_cgroup *prev,
+ struct mem_cgroup_reclaim_cookie *reclaim,
+ bool online)
+{
+ return NULL;
+}
+
static inline void mem_cgroup_iter_break(struct mem_cgroup *root,
struct mem_cgroup *prev)
{
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 470821d1ba1a..b1fb96233fa1 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1111,10 +1111,11 @@ struct mem_cgroup *get_mem_cgroup_from_current(void)
}
/**
- * mem_cgroup_iter - iterate over memory cgroup hierarchy
+ * mem_cgroup_iter_online - iterate over memory cgroup hierarchy
* @root: hierarchy root
* @prev: previously returned memcg, NULL on first invocation
* @reclaim: cookie for shared reclaim walks, NULL for full walks
+ * @online: whether to skip offline memcgs
*
* Returns references to children of the hierarchy below @root, or
* @root itself, or %NULL after a full round-trip.
@@ -1123,13 +1124,16 @@ struct mem_cgroup *get_mem_cgroup_from_current(void)
* invocations for reference counting, or use mem_cgroup_iter_break()
* to cancel a hierarchy walk before the round-trip is complete.
*
+ * Caller can skip offline memcgs by passing true for @online.
+ *
* Reclaimers can specify a node in @reclaim to divide up the memcgs
* in the hierarchy among all concurrent reclaimers operating on the
* same node.
*/
-struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
+struct mem_cgroup *mem_cgroup_iter_online(struct mem_cgroup *root,
struct mem_cgroup *prev,
- struct mem_cgroup_reclaim_cookie *reclaim)
+ struct mem_cgroup_reclaim_cookie *reclaim,
+ bool online)
{
struct mem_cgroup_reclaim_iter *iter;
struct cgroup_subsys_state *css = NULL;
@@ -1199,7 +1203,8 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
* is provided by the caller, so we know it's alive
* and kicking, and don't take an extra reference.
*/
- if (css == &root->css || css_tryget(css)) {
+ if (css == &root->css || (!online && css_tryget(css)) ||
+ css_tryget_online(css)) {
memcg = mem_cgroup_from_css(css);
break;
}
@@ -1228,6 +1233,22 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
return memcg;
}
+/**
+ * mem_cgroup_iter - iterate over memory cgroup hierarchy
+ * @root: hierarchy root
+ * @prev: previously returned memcg, NULL on first invocation
+ * @reclaim: cookie for shared reclaim walks, NULL for full walks
+ *
+ * Perform an iteration on the memory cgroup hierarchy without skipping
+ * offline memcgs.
+ */
+struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
+ struct mem_cgroup *prev,
+ struct mem_cgroup_reclaim_cookie *reclaim)
+{
+ return mem_cgroup_iter_online(root, prev, reclaim, false);
+}
+
/**
* mem_cgroup_iter_break - abort a hierarchy walk prematurely
* @root: hierarchy root
--
2.34.1
From: Domenico Cerasuolo <[email protected]>
Since zswap now writes back pages from memcg-specific LRUs, we now need a
new stat to show writebacks count for each memcg.
Suggested-by: Nhat Pham <[email protected]>
Signed-off-by: Domenico Cerasuolo <[email protected]>
Signed-off-by: Nhat Pham <[email protected]>
---
include/linux/vm_event_item.h | 1 +
mm/memcontrol.c | 1 +
mm/vmstat.c | 1 +
mm/zswap.c | 3 +++
4 files changed, 6 insertions(+)
diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index d1b847502f09..f4569ad98edf 100644
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -142,6 +142,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
#ifdef CONFIG_ZSWAP
ZSWPIN,
ZSWPOUT,
+ ZSWP_WB,
#endif
#ifdef CONFIG_X86
DIRECT_MAP_LEVEL2_SPLIT,
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 8c0f3f971179..f88c8fd03689 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -703,6 +703,7 @@ static const unsigned int memcg_vm_event_stat[] = {
#if defined(CONFIG_MEMCG_KMEM) && defined(CONFIG_ZSWAP)
ZSWPIN,
ZSWPOUT,
+ ZSWP_WB,
#endif
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
THP_FAULT_ALLOC,
diff --git a/mm/vmstat.c b/mm/vmstat.c
index afa5a38fcc9c..2249f85e4a87 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1401,6 +1401,7 @@ const char * const vmstat_text[] = {
#ifdef CONFIG_ZSWAP
"zswpin",
"zswpout",
+ "zswp_wb",
#endif
#ifdef CONFIG_X86
"direct_map_level2_splits",
diff --git a/mm/zswap.c b/mm/zswap.c
index 5e397fc1f375..6a761753f979 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -754,6 +754,9 @@ static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_o
}
zswap_written_back_pages++;
+ if (entry->objcg)
+ count_objcg_event(entry->objcg, ZSWP_WB);
+
/*
* Writeback started successfully, the page now belongs to the
* swapcache. Drop the entry from zswap - unless invalidate already
--
2.34.1
From: Domenico Cerasuolo <[email protected]>
Currently, we only have a single global LRU for zswap. This makes it
impossible to perform worload-specific shrinking - an memcg cannot
determine which pages in the pool it owns, and often ends up writing
pages from other memcgs. This issue has been previously observed in
practice and mitigated by simply disabling memcg-initiated shrinking:
https://lore.kernel.org/all/[email protected]/T/#u
This patch fully resolves the issue by replacing the global zswap LRU
with memcg- and NUMA-specific LRUs, and modify the reclaim logic:
a) When a store attempt hits an memcg limit, it now triggers a
synchronous reclaim attempt that, if successful, allows the new
hotter page to be accepted by zswap.
b) If the store attempt instead hits the global zswap limit, it will
trigger an asynchronous reclaim attempt, in which an memcg is
selected for reclaim in a round-robin-like fashion.
Signed-off-by: Domenico Cerasuolo <[email protected]>
Co-developed-by: Nhat Pham <[email protected]>
Signed-off-by: Nhat Pham <[email protected]>
---
include/linux/memcontrol.h | 5 +
include/linux/zswap.h | 2 +
mm/memcontrol.c | 2 +
mm/swap.h | 3 +-
mm/swap_state.c | 24 +++-
mm/zswap.c | 248 +++++++++++++++++++++++++++++--------
6 files changed, 223 insertions(+), 61 deletions(-)
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 5bfe41840e80..a568f70a2677 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1191,6 +1191,11 @@ static inline struct mem_cgroup *page_memcg_check(struct page *page)
return NULL;
}
+static inline struct mem_cgroup *get_mem_cgroup_from_objcg(struct obj_cgroup *objcg)
+{
+ return NULL;
+}
+
static inline bool folio_memcg_kmem(struct folio *folio)
{
return false;
diff --git a/include/linux/zswap.h b/include/linux/zswap.h
index 2a60ce39cfde..e571e393669b 100644
--- a/include/linux/zswap.h
+++ b/include/linux/zswap.h
@@ -15,6 +15,7 @@ bool zswap_load(struct folio *folio);
void zswap_invalidate(int type, pgoff_t offset);
void zswap_swapon(int type);
void zswap_swapoff(int type);
+void zswap_memcg_offline_cleanup(struct mem_cgroup *memcg);
#else
@@ -31,6 +32,7 @@ static inline bool zswap_load(struct folio *folio)
static inline void zswap_invalidate(int type, pgoff_t offset) {}
static inline void zswap_swapon(int type) {}
static inline void zswap_swapoff(int type) {}
+static inline void zswap_memcg_offline_cleanup(struct mem_cgroup *memcg) {}
#endif
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b1fb96233fa1..8c0f3f971179 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5635,6 +5635,8 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
page_counter_set_min(&memcg->memory, 0);
page_counter_set_low(&memcg->memory, 0);
+ zswap_memcg_offline_cleanup(memcg);
+
memcg_offline_kmem(memcg);
reparent_shrinker_deferred(memcg);
wb_memcg_offline(memcg);
diff --git a/mm/swap.h b/mm/swap.h
index 73c332ee4d91..c0dc73e10e91 100644
--- a/mm/swap.h
+++ b/mm/swap.h
@@ -51,7 +51,8 @@ struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
struct swap_iocb **plug);
struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
struct mempolicy *mpol, pgoff_t ilx,
- bool *new_page_allocated);
+ bool *new_page_allocated,
+ bool skip_if_exists);
struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t flag,
struct mempolicy *mpol, pgoff_t ilx);
struct page *swapin_readahead(swp_entry_t entry, gfp_t flag,
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 85d9e5806a6a..6c84236382f3 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -412,7 +412,8 @@ struct folio *filemap_get_incore_folio(struct address_space *mapping,
struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
struct mempolicy *mpol, pgoff_t ilx,
- bool *new_page_allocated)
+ bool *new_page_allocated,
+ bool skip_if_exists)
{
struct swap_info_struct *si;
struct folio *folio;
@@ -470,6 +471,17 @@ struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
if (err != -EEXIST)
goto fail_put_swap;
+ /*
+ * Protect against a recursive call to __read_swap_cache_async()
+ * on the same entry waiting forever here because SWAP_HAS_CACHE
+ * is set but the folio is not the swap cache yet. This can
+ * happen today if mem_cgroup_swapin_charge_folio() below
+ * triggers reclaim through zswap, which may call
+ * __read_swap_cache_async() in the writeback path.
+ */
+ if (skip_if_exists)
+ goto fail_put_swap;
+
/*
* We might race against __delete_from_swap_cache(), and
* stumble across a swap_map entry whose SWAP_HAS_CACHE
@@ -537,7 +549,7 @@ struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
mpol = get_vma_policy(vma, addr, 0, &ilx);
page = __read_swap_cache_async(entry, gfp_mask, mpol, ilx,
- &page_allocated);
+ &page_allocated, false);
mpol_cond_put(mpol);
if (page_allocated)
@@ -654,7 +666,7 @@ struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
/* Ok, do the async read-ahead now */
page = __read_swap_cache_async(
swp_entry(swp_type(entry), offset),
- gfp_mask, mpol, ilx, &page_allocated);
+ gfp_mask, mpol, ilx, &page_allocated, false);
if (!page)
continue;
if (page_allocated) {
@@ -672,7 +684,7 @@ struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
skip:
/* The page was likely read above, so no need for plugging here */
page = __read_swap_cache_async(entry, gfp_mask, mpol, ilx,
- &page_allocated);
+ &page_allocated, false);
if (unlikely(page_allocated))
swap_readpage(page, false, NULL);
return page;
@@ -827,7 +839,7 @@ static struct page *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask,
pte_unmap(pte);
pte = NULL;
page = __read_swap_cache_async(entry, gfp_mask, mpol, ilx,
- &page_allocated);
+ &page_allocated, false);
if (!page)
continue;
if (page_allocated) {
@@ -847,7 +859,7 @@ static struct page *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask,
skip:
/* The page was likely read above, so no need for plugging here */
page = __read_swap_cache_async(targ_entry, gfp_mask, mpol, targ_ilx,
- &page_allocated);
+ &page_allocated, false);
if (unlikely(page_allocated))
swap_readpage(page, false, NULL);
return page;
diff --git a/mm/zswap.c b/mm/zswap.c
index 4bdb2d83bb0d..5e397fc1f375 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -35,6 +35,7 @@
#include <linux/writeback.h>
#include <linux/pagemap.h>
#include <linux/workqueue.h>
+#include <linux/list_lru.h>
#include "swap.h"
#include "internal.h"
@@ -174,8 +175,8 @@ struct zswap_pool {
struct work_struct shrink_work;
struct hlist_node node;
char tfm_name[CRYPTO_MAX_ALG_NAME];
- struct list_head lru;
- spinlock_t lru_lock;
+ struct list_lru list_lru;
+ struct mem_cgroup *next_shrink;
};
/*
@@ -291,15 +292,40 @@ static void zswap_update_total_size(void)
zswap_pool_total_size = total;
}
+/* should be called under RCU */
+static inline struct mem_cgroup *mem_cgroup_from_entry(struct zswap_entry *entry)
+{
+ return entry->objcg ? obj_cgroup_memcg(entry->objcg) : NULL;
+}
+
+static inline int entry_to_nid(struct zswap_entry *entry)
+{
+ return page_to_nid(virt_to_page(entry));
+}
+
+void zswap_memcg_offline_cleanup(struct mem_cgroup *memcg)
+{
+ struct zswap_pool *pool;
+
+ /* lock out zswap pools list modification */
+ spin_lock(&zswap_pools_lock);
+ list_for_each_entry(pool, &zswap_pools, list) {
+ if (pool->next_shrink == memcg)
+ pool->next_shrink =
+ mem_cgroup_iter_online(NULL, pool->next_shrink, NULL, true);
+ }
+ spin_unlock(&zswap_pools_lock);
+}
+
/*********************************
* zswap entry functions
**********************************/
static struct kmem_cache *zswap_entry_cache;
-static struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp)
+static struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp, int nid)
{
struct zswap_entry *entry;
- entry = kmem_cache_alloc(zswap_entry_cache, gfp);
+ entry = kmem_cache_alloc_node(zswap_entry_cache, gfp, nid);
if (!entry)
return NULL;
entry->refcount = 1;
@@ -312,6 +338,61 @@ static void zswap_entry_cache_free(struct zswap_entry *entry)
kmem_cache_free(zswap_entry_cache, entry);
}
+/*********************************
+* lru functions
+**********************************/
+static void zswap_lru_add(struct list_lru *list_lru, struct zswap_entry *entry)
+{
+ int nid = entry_to_nid(entry);
+ struct mem_cgroup *memcg;
+
+ /*
+ * Note that it is safe to use rcu_read_lock() here, even in the face of
+ * concurrent memcg offlining. Thanks to the memcg->kmemcg_id indirection
+ * used in list_lru lookup, only two scenarios are possible:
+ *
+ * 1. list_lru_add() is called before memcg->kmemcg_id is updated. The
+ * new entry will be reparented to memcg's parent's list_lru.
+ * 2. list_lru_add() is called after memcg->kmemcg_id is updated. The
+ * new entry will be added directly to memcg's parent's list_lru.
+ *
+ * Similar reasoning holds for list_lru_del() and list_lru_putback().
+ */
+ rcu_read_lock();
+ memcg = mem_cgroup_from_entry(entry);
+ /* will always succeed */
+ list_lru_add(list_lru, &entry->lru, nid, memcg);
+ rcu_read_unlock();
+}
+
+static void zswap_lru_del(struct list_lru *list_lru, struct zswap_entry *entry)
+{
+ int nid = entry_to_nid(entry);
+ struct mem_cgroup *memcg;
+
+ rcu_read_lock();
+ memcg = mem_cgroup_from_entry(entry);
+ /* will always succeed */
+ list_lru_del(list_lru, &entry->lru, nid, memcg);
+ rcu_read_unlock();
+}
+
+static void zswap_lru_putback(struct list_lru *list_lru,
+ struct zswap_entry *entry)
+{
+ int nid = entry_to_nid(entry);
+ spinlock_t *lock = &list_lru->node[nid].lock;
+ struct mem_cgroup *memcg;
+
+ rcu_read_lock();
+ memcg = mem_cgroup_from_entry(entry);
+ spin_lock(lock);
+ /* we cannot use list_lru_add here, because it increments node's lru count */
+ list_lru_putback(list_lru, &entry->lru, nid, memcg);
+ spin_unlock(lock);
+ rcu_read_unlock();
+}
+
/*********************************
* rbtree functions
**********************************/
@@ -396,9 +477,7 @@ static void zswap_free_entry(struct zswap_entry *entry)
if (!entry->length)
atomic_dec(&zswap_same_filled_pages);
else {
- spin_lock(&entry->pool->lru_lock);
- list_del(&entry->lru);
- spin_unlock(&entry->pool->lru_lock);
+ zswap_lru_del(&entry->pool->list_lru, entry);
zpool_free(zswap_find_zpool(entry), entry->handle);
zswap_pool_put(entry->pool);
}
@@ -632,21 +711,15 @@ static void zswap_invalidate_entry(struct zswap_tree *tree,
zswap_entry_put(tree, entry);
}
-static int zswap_reclaim_entry(struct zswap_pool *pool)
+static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_one *l,
+ spinlock_t *lock, void *arg)
{
- struct zswap_entry *entry;
+ struct zswap_entry *entry = container_of(item, struct zswap_entry, lru);
struct zswap_tree *tree;
pgoff_t swpoffset;
- int ret;
+ enum lru_status ret = LRU_REMOVED_RETRY;
+ int writeback_result;
- /* Get an entry off the LRU */
- spin_lock(&pool->lru_lock);
- if (list_empty(&pool->lru)) {
- spin_unlock(&pool->lru_lock);
- return -EINVAL;
- }
- entry = list_last_entry(&pool->lru, struct zswap_entry, lru);
- list_del_init(&entry->lru);
/*
* Once the lru lock is dropped, the entry might get freed. The
* swpoffset is copied to the stack, and entry isn't deref'd again
@@ -654,28 +727,32 @@ static int zswap_reclaim_entry(struct zswap_pool *pool)
*/
swpoffset = swp_offset(entry->swpentry);
tree = zswap_trees[swp_type(entry->swpentry)];
- spin_unlock(&pool->lru_lock);
+ list_lru_isolate(l, item);
+ /*
+ * It's safe to drop the lock here because we return either
+ * LRU_REMOVED_RETRY or LRU_RETRY.
+ */
+ spin_unlock(lock);
/* Check for invalidate() race */
spin_lock(&tree->lock);
- if (entry != zswap_rb_search(&tree->rbroot, swpoffset)) {
- ret = -EAGAIN;
+ if (entry != zswap_rb_search(&tree->rbroot, swpoffset))
goto unlock;
- }
+
/* Hold a reference to prevent a free during writeback */
zswap_entry_get(entry);
spin_unlock(&tree->lock);
- ret = zswap_writeback_entry(entry, tree);
+ writeback_result = zswap_writeback_entry(entry, tree);
spin_lock(&tree->lock);
- if (ret) {
- /* Writeback failed, put entry back on LRU */
- spin_lock(&pool->lru_lock);
- list_move(&entry->lru, &pool->lru);
- spin_unlock(&pool->lru_lock);
+ if (writeback_result) {
+ zswap_reject_reclaim_fail++;
+ zswap_lru_putback(&entry->pool->list_lru, entry);
+ ret = LRU_RETRY;
goto put_unlock;
}
+ zswap_written_back_pages++;
/*
* Writeback started successfully, the page now belongs to the
@@ -689,27 +766,76 @@ static int zswap_reclaim_entry(struct zswap_pool *pool)
zswap_entry_put(tree, entry);
unlock:
spin_unlock(&tree->lock);
- return ret ? -EAGAIN : 0;
+ spin_lock(lock);
+ return ret;
+}
+
+static int shrink_memcg(struct mem_cgroup *memcg)
+{
+ struct zswap_pool *pool;
+ int nid, shrunk = 0;
+
+ /*
+ * Skip zombies because their LRUs are reparented and we would be
+ * reclaiming from the parent instead of the dead memcg.
+ */
+ if (memcg && !mem_cgroup_online(memcg))
+ return -ENOENT;
+
+ pool = zswap_pool_current_get();
+ if (!pool)
+ return -EINVAL;
+
+ for_each_node_state(nid, N_NORMAL_MEMORY) {
+ unsigned long nr_to_walk = 1;
+
+ shrunk += list_lru_walk_one(&pool->list_lru, nid, memcg,
+ &shrink_memcg_cb, NULL, &nr_to_walk);
+ }
+ zswap_pool_put(pool);
+ return shrunk ? 0 : -EAGAIN;
}
static void shrink_worker(struct work_struct *w)
{
struct zswap_pool *pool = container_of(w, typeof(*pool),
shrink_work);
+ struct mem_cgroup *memcg;
int ret, failures = 0;
+ /* global reclaim will select cgroup in a round-robin fashion. */
do {
- ret = zswap_reclaim_entry(pool);
- if (ret) {
- zswap_reject_reclaim_fail++;
- if (ret != -EAGAIN)
- break;
+ spin_lock(&zswap_pools_lock);
+ memcg = pool->next_shrink =
+ mem_cgroup_iter_online(NULL, pool->next_shrink, NULL, true);
+
+ /* full round trip */
+ if (!memcg) {
+ spin_unlock(&zswap_pools_lock);
if (++failures == MAX_RECLAIM_RETRIES)
break;
+
+ goto resched;
}
+
+ /*
+ * Acquire an extra reference to the iterated memcg in case the
+ * original reference is dropped by the zswap offlining callback.
+ */
+ css_get(&memcg->css);
+ spin_unlock(&zswap_pools_lock);
+
+ ret = shrink_memcg(memcg);
+ mem_cgroup_put(memcg);
+
+ if (ret == -EINVAL)
+ break;
+ if (ret && ++failures == MAX_RECLAIM_RETRIES)
+ break;
+
+resched:
cond_resched();
} while (!zswap_can_accept());
- zswap_pool_put(pool);
}
static struct zswap_pool *zswap_pool_create(char *type, char *compressor)
@@ -767,8 +893,7 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor)
*/
kref_init(&pool->kref);
INIT_LIST_HEAD(&pool->list);
- INIT_LIST_HEAD(&pool->lru);
- spin_lock_init(&pool->lru_lock);
+ list_lru_init_memcg(&pool->list_lru, NULL);
INIT_WORK(&pool->shrink_work, shrink_worker);
zswap_pool_debug("created", pool);
@@ -834,6 +959,13 @@ static void zswap_pool_destroy(struct zswap_pool *pool)
cpuhp_state_remove_instance(CPUHP_MM_ZSWP_POOL_PREPARE, &pool->node);
free_percpu(pool->acomp_ctx);
+ list_lru_destroy(&pool->list_lru);
+
+ spin_lock(&zswap_pools_lock);
+ mem_cgroup_put(pool->next_shrink);
+ pool->next_shrink = NULL;
+ spin_unlock(&zswap_pools_lock);
+
for (i = 0; i < ZSWAP_NR_ZPOOLS; i++)
zpool_destroy_pool(pool->zpools[i]);
kfree(pool);
@@ -1081,7 +1213,7 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
/* try to allocate swap cache page */
mpol = get_task_policy(current);
page = __read_swap_cache_async(swpentry, GFP_KERNEL, mpol,
- NO_INTERLEAVE_INDEX, &page_was_allocated);
+ NO_INTERLEAVE_INDEX, &page_was_allocated, true);
if (!page) {
ret = -ENOMEM;
goto fail;
@@ -1152,7 +1284,6 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
/* start writeback */
__swap_writepage(page, &wbc);
put_page(page);
- zswap_written_back_pages++;
return ret;
@@ -1209,6 +1340,7 @@ bool zswap_store(struct folio *folio)
struct scatterlist input, output;
struct crypto_acomp_ctx *acomp_ctx;
struct obj_cgroup *objcg = NULL;
+ struct mem_cgroup *memcg = NULL;
struct zswap_pool *pool;
struct zpool *zpool;
unsigned int dlen = PAGE_SIZE;
@@ -1240,15 +1372,15 @@ bool zswap_store(struct folio *folio)
zswap_invalidate_entry(tree, dupentry);
}
spin_unlock(&tree->lock);
-
- /*
- * XXX: zswap reclaim does not work with cgroups yet. Without a
- * cgroup-aware entry LRU, we will push out entries system-wide based on
- * local cgroup limits.
- */
objcg = get_obj_cgroup_from_folio(folio);
- if (objcg && !obj_cgroup_may_zswap(objcg))
- goto reject;
+ if (objcg && !obj_cgroup_may_zswap(objcg)) {
+ memcg = get_mem_cgroup_from_objcg(objcg);
+ if (shrink_memcg(memcg)) {
+ mem_cgroup_put(memcg);
+ goto reject;
+ }
+ mem_cgroup_put(memcg);
+ }
/* reclaim space if needed */
if (zswap_is_full()) {
@@ -1265,7 +1397,7 @@ bool zswap_store(struct folio *folio)
}
/* allocate entry */
- entry = zswap_entry_cache_alloc(GFP_KERNEL);
+ entry = zswap_entry_cache_alloc(GFP_KERNEL, page_to_nid(page));
if (!entry) {
zswap_reject_kmemcache_fail++;
goto reject;
@@ -1292,6 +1424,15 @@ bool zswap_store(struct folio *folio)
if (!entry->pool)
goto freepage;
+ if (objcg) {
+ memcg = get_mem_cgroup_from_objcg(objcg);
+ if (memcg_list_lru_alloc(memcg, &entry->pool->list_lru, GFP_KERNEL)) {
+ mem_cgroup_put(memcg);
+ goto put_pool;
+ }
+ mem_cgroup_put(memcg);
+ }
+
/* compress */
acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
@@ -1370,9 +1511,8 @@ bool zswap_store(struct folio *folio)
zswap_invalidate_entry(tree, dupentry);
}
if (entry->length) {
- spin_lock(&entry->pool->lru_lock);
- list_add(&entry->lru, &entry->pool->lru);
- spin_unlock(&entry->pool->lru_lock);
+ INIT_LIST_HEAD(&entry->lru);
+ zswap_lru_add(&entry->pool->list_lru, entry);
}
spin_unlock(&tree->lock);
@@ -1385,6 +1525,7 @@ bool zswap_store(struct folio *folio)
put_dstmem:
mutex_unlock(acomp_ctx->mutex);
+put_pool:
zswap_pool_put(entry->pool);
freepage:
zswap_entry_cache_free(entry);
@@ -1479,9 +1620,8 @@ bool zswap_load(struct folio *folio)
zswap_invalidate_entry(tree, entry);
folio_mark_dirty(folio);
} else if (entry->length) {
- spin_lock(&entry->pool->lru_lock);
- list_move(&entry->lru, &entry->pool->lru);
- spin_unlock(&entry->pool->lru_lock);
+ zswap_lru_del(&entry->pool->list_lru, entry);
+ zswap_lru_add(&entry->pool->list_lru, entry);
}
zswap_entry_put(tree, entry);
spin_unlock(&tree->lock);
--
2.34.1
Currently, we only shrink the zswap pool when the user-defined limit is
hit. This means that if we set the limit too high, cold data that are
unlikely to be used again will reside in the pool, wasting precious
memory. It is hard to predict how much zswap space will be needed ahead
of time, as this depends on the workload (specifically, on factors such
as memory access patterns and compressibility of the memory pages).
This patch implements a memcg- and NUMA-aware shrinker for zswap, that
is initiated when there is memory pressure. The shrinker does not
have any parameter that must be tuned by the user, and can be opted in
or out on a per-memcg basis.
Furthermore, to make it more robust for many workloads and prevent
overshrinking (i.e evicting warm pages that might be refaulted into
memory), we build in the following heuristics:
* Estimate the number of warm pages residing in zswap, and attempt to
protect this region of the zswap LRU.
* Scale the number of freeable objects by an estimate of the memory
saving factor. The better zswap compresses the data, the fewer pages
we will evict to swap (as we will otherwise incur IO for relatively
small memory saving).
* During reclaim, if the shrinker encounters a page that is also being
brought into memory, the shrinker will cautiously terminate its
shrinking action, as this is a sign that it is touching the warmer
region of the zswap LRU.
As a proof of concept, we ran the following synthetic benchmark:
build the linux kernel in a memory-limited cgroup, and allocate some
cold data in tmpfs to see if the shrinker could write them out and
improved the overall performance. Depending on the amount of cold data
generated, we observe from 14% to 35% reduction in kernel CPU time used
in the kernel builds.
Signed-off-by: Nhat Pham <[email protected]>
---
Documentation/admin-guide/mm/zswap.rst | 7 +
include/linux/mmzone.h | 2 +
include/linux/zswap.h | 25 +++-
mm/mmzone.c | 1 +
mm/swap_state.c | 2 +
mm/zswap.c | 177 ++++++++++++++++++++++++-
6 files changed, 208 insertions(+), 6 deletions(-)
diff --git a/Documentation/admin-guide/mm/zswap.rst b/Documentation/admin-guide/mm/zswap.rst
index 45b98390e938..522ae22ccb84 100644
--- a/Documentation/admin-guide/mm/zswap.rst
+++ b/Documentation/admin-guide/mm/zswap.rst
@@ -153,6 +153,13 @@ attribute, e. g.::
Setting this parameter to 100 will disable the hysteresis.
+When there is a sizable amount of cold memory residing in the zswap pool, it
+can be advantageous to proactively write these cold pages to swap and reclaim
+the memory for other use cases. By default, the zswap shrinker is disabled.
+User can enable it as follows:
+
+ echo Y > /sys/module/zswap/parameters/shrinker_enabled
+
A debugfs interface is provided for various statistic about pool size, number
of pages stored, same-value filled pages and various counters for the reasons
pages are rejected.
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 7b1816450bfc..b23bc5390240 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -22,6 +22,7 @@
#include <linux/mm_types.h>
#include <linux/page-flags.h>
#include <linux/local_lock.h>
+#include <linux/zswap.h>
#include <asm/page.h>
/* Free memory management - zoned buddy allocator. */
@@ -641,6 +642,7 @@ struct lruvec {
#ifdef CONFIG_MEMCG
struct pglist_data *pgdat;
#endif
+ struct zswap_lruvec_state zswap_lruvec_state;
};
/* Isolate for asynchronous migration */
diff --git a/include/linux/zswap.h b/include/linux/zswap.h
index e571e393669b..03253a5965bb 100644
--- a/include/linux/zswap.h
+++ b/include/linux/zswap.h
@@ -5,20 +5,40 @@
#include <linux/types.h>
#include <linux/mm_types.h>
+struct lruvec;
+
extern u64 zswap_pool_total_size;
extern atomic_t zswap_stored_pages;
#ifdef CONFIG_ZSWAP
+struct zswap_lruvec_state {
+ /*
+ * Number of pages in zswap that should be protected from the shrinker.
+ * This number is an estimate of the following counts:
+ *
+ * a) Recent page faults.
+ * b) Recent insertion to the zswap LRU. This includes new zswap stores,
+ * as well as recent zswap LRU rotations.
+ *
+ * These pages are likely to be warm, and might incur IO if the are written
+ * to swap.
+ */
+ atomic_long_t nr_zswap_protected;
+};
+
bool zswap_store(struct folio *folio);
bool zswap_load(struct folio *folio);
void zswap_invalidate(int type, pgoff_t offset);
void zswap_swapon(int type);
void zswap_swapoff(int type);
void zswap_memcg_offline_cleanup(struct mem_cgroup *memcg);
-
+void zswap_lruvec_state_init(struct lruvec *lruvec);
+void zswap_lruvec_swapin(struct page *page);
#else
+struct zswap_lruvec_state {};
+
static inline bool zswap_store(struct folio *folio)
{
return false;
@@ -33,7 +53,8 @@ static inline void zswap_invalidate(int type, pgoff_t offset) {}
static inline void zswap_swapon(int type) {}
static inline void zswap_swapoff(int type) {}
static inline void zswap_memcg_offline_cleanup(struct mem_cgroup *memcg) {}
-
+static inline void zswap_lruvec_state_init(struct lruvec *lruvec) {}
+static inline void zswap_lruvec_swapin(struct page *page) {}
#endif
#endif /* _LINUX_ZSWAP_H */
diff --git a/mm/mmzone.c b/mm/mmzone.c
index b594d3f268fe..c01896eca736 100644
--- a/mm/mmzone.c
+++ b/mm/mmzone.c
@@ -78,6 +78,7 @@ void lruvec_init(struct lruvec *lruvec)
memset(lruvec, 0, sizeof(struct lruvec));
spin_lock_init(&lruvec->lru_lock);
+ zswap_lruvec_state_init(lruvec);
for_each_lru(lru)
INIT_LIST_HEAD(&lruvec->lists[lru]);
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 6c84236382f3..94ed2d508db0 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -687,6 +687,7 @@ struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
&page_allocated, false);
if (unlikely(page_allocated))
swap_readpage(page, false, NULL);
+ zswap_lruvec_swapin(page);
return page;
}
@@ -862,6 +863,7 @@ static struct page *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask,
&page_allocated, false);
if (unlikely(page_allocated))
swap_readpage(page, false, NULL);
+ zswap_lruvec_swapin(page);
return page;
}
diff --git a/mm/zswap.c b/mm/zswap.c
index 6a761753f979..a3378b4c8e6e 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -148,6 +148,10 @@ module_param_named(exclusive_loads, zswap_exclusive_loads_enabled, bool, 0644);
/* Number of zpools in zswap_pool (empirically determined for scalability) */
#define ZSWAP_NR_ZPOOLS 32
+/* Enable/disable memory pressure-based shrinker. */
+static bool zswap_shrinker_enabled;
+module_param_named(shrinker_enabled, zswap_shrinker_enabled, bool, 0644);
+
/*********************************
* data structures
**********************************/
@@ -177,6 +181,8 @@ struct zswap_pool {
char tfm_name[CRYPTO_MAX_ALG_NAME];
struct list_lru list_lru;
struct mem_cgroup *next_shrink;
+ struct shrinker *shrinker;
+ atomic_t nr_stored;
};
/*
@@ -275,17 +281,26 @@ static bool zswap_can_accept(void)
DIV_ROUND_UP(zswap_pool_total_size, PAGE_SIZE);
}
+static u64 get_zswap_pool_size(struct zswap_pool *pool)
+{
+ u64 pool_size = 0;
+ int i;
+
+ for (i = 0; i < ZSWAP_NR_ZPOOLS; i++)
+ pool_size += zpool_get_total_size(pool->zpools[i]);
+
+ return pool_size;
+}
+
static void zswap_update_total_size(void)
{
struct zswap_pool *pool;
u64 total = 0;
- int i;
rcu_read_lock();
list_for_each_entry_rcu(pool, &zswap_pools, list)
- for (i = 0; i < ZSWAP_NR_ZPOOLS; i++)
- total += zpool_get_total_size(pool->zpools[i]);
+ total += get_zswap_pool_size(pool);
rcu_read_unlock();
@@ -338,13 +353,34 @@ static void zswap_entry_cache_free(struct zswap_entry *entry)
kmem_cache_free(zswap_entry_cache, entry);
}
+/*********************************
+* zswap lruvec functions
+**********************************/
+void zswap_lruvec_state_init(struct lruvec *lruvec)
+{
+ atomic_long_set(&lruvec->zswap_lruvec_state.nr_zswap_protected, 0);
+}
+
+void zswap_lruvec_swapin(struct page *page)
+{
+ struct lruvec *lruvec;
+
+ if (page) {
+ lruvec = folio_lruvec(page_folio(page));
+ atomic_long_inc(&lruvec->zswap_lruvec_state.nr_zswap_protected);
+ }
+}
+
/*********************************
* lru functions
**********************************/
static void zswap_lru_add(struct list_lru *list_lru, struct zswap_entry *entry)
{
+ atomic_long_t *nr_zswap_protected;
+ unsigned long lru_size, old, new;
int nid = entry_to_nid(entry);
struct mem_cgroup *memcg;
+ struct lruvec *lruvec;
/*
* Note that it is safe to use rcu_read_lock() here, even in the face of
@@ -362,6 +398,19 @@ static void zswap_lru_add(struct list_lru *list_lru, struct zswap_entry *entry)
memcg = mem_cgroup_from_entry(entry);
/* will always succeed */
list_lru_add(list_lru, &entry->lru, nid, memcg);
+
+ /* Update the protection area */
+ lru_size = list_lru_count_one(list_lru, nid, memcg);
+ lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(nid));
+ nr_zswap_protected = &lruvec->zswap_lruvec_state.nr_zswap_protected;
+ old = atomic_long_inc_return(nr_zswap_protected);
+ /*
+ * Decay to avoid overflow and adapt to changing workloads.
+ * This is based on LRU reclaim cost decaying heuristics.
+ */
+ do {
+ new = old > lru_size / 4 ? old / 2 : old;
+ } while (!atomic_long_try_cmpxchg(nr_zswap_protected, &old, new));
rcu_read_unlock();
}
@@ -383,6 +432,7 @@ static void zswap_lru_putback(struct list_lru *list_lru,
int nid = entry_to_nid(entry);
spinlock_t *lock = &list_lru->node[nid].lock;
struct mem_cgroup *memcg;
+ struct lruvec *lruvec;
rcu_read_lock();
memcg = mem_cgroup_from_entry(entry);
@@ -390,6 +440,10 @@ static void zswap_lru_putback(struct list_lru *list_lru,
/* we cannot use list_lru_add here, because it increments node's lru count */
list_lru_putback(list_lru, &entry->lru, nid, memcg);
spin_unlock(lock);
+
+ lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(entry_to_nid(entry)));
+ /* increment the protection area to account for the LRU rotation. */
+ atomic_long_inc(&lruvec->zswap_lruvec_state.nr_zswap_protected);
rcu_read_unlock();
}
@@ -479,6 +533,7 @@ static void zswap_free_entry(struct zswap_entry *entry)
else {
zswap_lru_del(&entry->pool->list_lru, entry);
zpool_free(zswap_find_zpool(entry), entry->handle);
+ atomic_dec(&entry->pool->nr_stored);
zswap_pool_put(entry->pool);
}
zswap_entry_cache_free(entry);
@@ -520,6 +575,95 @@ static struct zswap_entry *zswap_entry_find_get(struct rb_root *root,
return entry;
}
+/*********************************
+* shrinker functions
+**********************************/
+static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_one *l,
+ spinlock_t *lock, void *arg);
+
+static unsigned long zswap_shrinker_scan(struct shrinker *shrinker,
+ struct shrink_control *sc)
+{
+ struct lruvec *lruvec = mem_cgroup_lruvec(sc->memcg, NODE_DATA(sc->nid));
+ unsigned long shrink_ret, nr_protected, lru_size;
+ struct zswap_pool *pool = shrinker->private_data;
+ bool encountered_page_in_swapcache = false;
+
+ nr_protected =
+ atomic_long_read(&lruvec->zswap_lruvec_state.nr_zswap_protected);
+ lru_size = list_lru_shrink_count(&pool->list_lru, sc);
+
+ /*
+ * Abort if the shrinker is disabled or if we are shrinking into the
+ * protected region.
+ */
+ if (!zswap_shrinker_enabled || nr_protected >= lru_size - sc->nr_to_scan) {
+ sc->nr_scanned = 0;
+ return SHRINK_STOP;
+ }
+
+ shrink_ret = list_lru_shrink_walk(&pool->list_lru, sc, &shrink_memcg_cb,
+ &encountered_page_in_swapcache);
+
+ if (encountered_page_in_swapcache)
+ return SHRINK_STOP;
+
+ return shrink_ret ? shrink_ret : SHRINK_STOP;
+}
+
+static unsigned long zswap_shrinker_count(struct shrinker *shrinker,
+ struct shrink_control *sc)
+{
+ struct zswap_pool *pool = shrinker->private_data;
+ struct mem_cgroup *memcg = sc->memcg;
+ struct lruvec *lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(sc->nid));
+ unsigned long nr_backing, nr_stored, nr_freeable, nr_protected;
+
+#ifdef CONFIG_MEMCG_KMEM
+ cgroup_rstat_flush(memcg->css.cgroup);
+ nr_backing = memcg_page_state(memcg, MEMCG_ZSWAP_B) >> PAGE_SHIFT;
+ nr_stored = memcg_page_state(memcg, MEMCG_ZSWAPPED);
+#else
+ /* use pool stats instead of memcg stats */
+ nr_backing = get_zswap_pool_size(pool) >> PAGE_SHIFT;
+ nr_stored = atomic_read(&pool->nr_stored);
+#endif
+
+ if (!zswap_shrinker_enabled || !nr_stored)
+ return 0;
+
+ nr_protected =
+ atomic_long_read(&lruvec->zswap_lruvec_state.nr_zswap_protected);
+ nr_freeable = list_lru_shrink_count(&pool->list_lru, sc);
+ /*
+ * Subtract the lru size by an estimate of the number of pages
+ * that should be protected.
+ */
+ nr_freeable = nr_freeable > nr_protected ? nr_freeable - nr_protected : 0;
+
+ /*
+ * Scale the number of freeable pages by the memory saving factor.
+ * This ensures that the better zswap compresses memory, the fewer
+ * pages we will evict to swap (as it will otherwise incur IO for
+ * relatively small memory saving).
+ */
+ return mult_frac(nr_freeable, nr_backing, nr_stored);
+}
+
+static void zswap_alloc_shrinker(struct zswap_pool *pool)
+{
+ pool->shrinker =
+ shrinker_alloc(SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE, "mm-zswap");
+ if (!pool->shrinker)
+ return;
+
+ pool->shrinker->private_data = pool;
+ pool->shrinker->scan_objects = zswap_shrinker_scan;
+ pool->shrinker->count_objects = zswap_shrinker_count;
+ pool->shrinker->batch = 0;
+ pool->shrinker->seeks = DEFAULT_SEEKS;
+}
+
/*********************************
* per-cpu code
**********************************/
@@ -715,6 +859,7 @@ static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_o
spinlock_t *lock, void *arg)
{
struct zswap_entry *entry = container_of(item, struct zswap_entry, lru);
+ bool *encountered_page_in_swapcache = (bool *)arg;
struct zswap_tree *tree;
pgoff_t swpoffset;
enum lru_status ret = LRU_REMOVED_RETRY;
@@ -750,6 +895,17 @@ static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_o
zswap_reject_reclaim_fail++;
zswap_lru_putback(&entry->pool->list_lru, entry);
ret = LRU_RETRY;
+
+ /*
+ * Encountering a page already in swap cache is a sign that we are shrinking
+ * into the warmer region. We should terminate shrinking (if we're in the dynamic
+ * shrinker context).
+ */
+ if (writeback_result == -EEXIST && encountered_page_in_swapcache) {
+ ret = LRU_SKIP;
+ *encountered_page_in_swapcache = true;
+ }
+
goto put_unlock;
}
zswap_written_back_pages++;
@@ -889,6 +1045,11 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor)
&pool->node);
if (ret)
goto error;
+
+ zswap_alloc_shrinker(pool);
+ if (!pool->shrinker)
+ goto error;
+
pr_debug("using %s compressor\n", pool->tfm_name);
/* being the current pool takes 1 ref; this func expects the
@@ -896,13 +1057,19 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor)
*/
kref_init(&pool->kref);
INIT_LIST_HEAD(&pool->list);
- list_lru_init_memcg(&pool->list_lru, NULL);
+ if (list_lru_init_memcg(&pool->list_lru, pool->shrinker))
+ goto lru_fail;
+ shrinker_register(pool->shrinker);
INIT_WORK(&pool->shrink_work, shrink_worker);
+ atomic_set(&pool->nr_stored, 0);
zswap_pool_debug("created", pool);
return pool;
+lru_fail:
+ list_lru_destroy(&pool->list_lru);
+ shrinker_free(pool->shrinker);
error:
if (pool->acomp_ctx)
free_percpu(pool->acomp_ctx);
@@ -960,6 +1127,7 @@ static void zswap_pool_destroy(struct zswap_pool *pool)
zswap_pool_debug("destroying", pool);
+ shrinker_free(pool->shrinker);
cpuhp_state_remove_instance(CPUHP_MM_ZSWP_POOL_PREPARE, &pool->node);
free_percpu(pool->acomp_ctx);
list_lru_destroy(&pool->list_lru);
@@ -1516,6 +1684,7 @@ bool zswap_store(struct folio *folio)
if (entry->length) {
INIT_LIST_HEAD(&entry->lru);
zswap_lru_add(&entry->pool->list_lru, entry);
+ atomic_inc(&entry->pool->nr_stored);
}
spin_unlock(&tree->lock);
--
2.34.1
From: Domenico Cerasuolo <[email protected]>
The memcg-zswap self test is updated to adjust to the behavior change
implemented by commit 87730b165089 ("zswap: make shrinking memcg-aware"),
where zswap performs writeback for specific memcg.
Signed-off-by: Domenico Cerasuolo <[email protected]>
Signed-off-by: Nhat Pham <[email protected]>
---
tools/testing/selftests/cgroup/test_zswap.c | 74 ++++++++++++++-------
1 file changed, 50 insertions(+), 24 deletions(-)
diff --git a/tools/testing/selftests/cgroup/test_zswap.c b/tools/testing/selftests/cgroup/test_zswap.c
index c99d2adaca3f..47fdaa146443 100644
--- a/tools/testing/selftests/cgroup/test_zswap.c
+++ b/tools/testing/selftests/cgroup/test_zswap.c
@@ -50,9 +50,9 @@ static int get_zswap_stored_pages(size_t *value)
return read_int("/sys/kernel/debug/zswap/stored_pages", value);
}
-static int get_zswap_written_back_pages(size_t *value)
+static int get_cg_wb_count(const char *cg)
{
- return read_int("/sys/kernel/debug/zswap/written_back_pages", value);
+ return cg_read_key_long(cg, "memory.stat", "zswp_wb");
}
static long get_zswpout(const char *cgroup)
@@ -73,6 +73,24 @@ static int allocate_bytes(const char *cgroup, void *arg)
return 0;
}
+static char *setup_test_group_1M(const char *root, const char *name)
+{
+ char *group_name = cg_name(root, name);
+
+ if (!group_name)
+ return NULL;
+ if (cg_create(group_name))
+ goto fail;
+ if (cg_write(group_name, "memory.max", "1M")) {
+ cg_destroy(group_name);
+ goto fail;
+ }
+ return group_name;
+fail:
+ free(group_name);
+ return NULL;
+}
+
/*
* Sanity test to check that pages are written into zswap.
*/
@@ -117,43 +135,51 @@ static int test_zswap_usage(const char *root)
/*
* When trying to store a memcg page in zswap, if the memcg hits its memory
- * limit in zswap, writeback should not be triggered.
- *
- * This was fixed with commit 0bdf0efa180a("zswap: do not shrink if cgroup may
- * not zswap"). Needs to be revised when a per memcg writeback mechanism is
- * implemented.
+ * limit in zswap, writeback should affect only the zswapped pages of that
+ * memcg.
*/
static int test_no_invasive_cgroup_shrink(const char *root)
{
- size_t written_back_before, written_back_after;
int ret = KSFT_FAIL;
- char *test_group;
+ size_t control_allocation_size = MB(10);
+ char *control_allocation, *wb_group = NULL, *control_group = NULL;
/* Set up */
- test_group = cg_name(root, "no_shrink_test");
- if (!test_group)
- goto out;
- if (cg_create(test_group))
+ wb_group = setup_test_group_1M(root, "per_memcg_wb_test1");
+ if (!wb_group)
+ return KSFT_FAIL;
+ if (cg_write(wb_group, "memory.zswap.max", "10K"))
goto out;
- if (cg_write(test_group, "memory.max", "1M"))
+ control_group = setup_test_group_1M(root, "per_memcg_wb_test2");
+ if (!control_group)
goto out;
- if (cg_write(test_group, "memory.zswap.max", "10K"))
+
+ /* Push some test_group2 memory into zswap */
+ if (cg_enter_current(control_group))
goto out;
- if (get_zswap_written_back_pages(&written_back_before))
+ control_allocation = malloc(control_allocation_size);
+ for (int i = 0; i < control_allocation_size; i += 4095)
+ control_allocation[i] = 'a';
+ if (cg_read_key_long(control_group, "memory.stat", "zswapped") < 1)
goto out;
- /* Allocate 10x memory.max to push memory into zswap */
- if (cg_run(test_group, allocate_bytes, (void *)MB(10)))
+ /* Allocate 10x memory.max to push wb_group memory into zswap and trigger wb */
+ if (cg_run(wb_group, allocate_bytes, (void *)MB(10)))
goto out;
- /* Verify that no writeback happened because of the memcg allocation */
- if (get_zswap_written_back_pages(&written_back_after))
- goto out;
- if (written_back_after == written_back_before)
+ /* Verify that only zswapped memory from gwb_group has been written back */
+ if (get_cg_wb_count(wb_group) > 0 && get_cg_wb_count(control_group) == 0)
ret = KSFT_PASS;
out:
- cg_destroy(test_group);
- free(test_group);
+ cg_enter_current(root);
+ if (control_group) {
+ cg_destroy(control_group);
+ free(control_group);
+ }
+ cg_destroy(wb_group);
+ free(wb_group);
+ if (control_allocation)
+ free(control_allocation);
return ret;
}
--
2.34.1
On Mon, Nov 27, 2023 at 03:45:55PM -0800, Nhat Pham wrote:
> The interface of list_lru is based on the assumption that the list node
> and the data it represents belong to the same allocated on the correct
> node/memcg. While this assumption is valid for existing slab objects LRU
> such as dentries and inodes, it is undocumented, and rather inflexible
> for certain potential list_lru users (such as the upcoming zswap
> shrinker and the THP shrinker). It has caused us a lot of issues during
> our development.
>
> This patch changes list_lru interface so that the caller must explicitly
> specify numa node and memcg when adding and removing objects. The old
> list_lru_add() and list_lru_del() are renamed to list_lru_add_obj() and
> list_lru_del_obj(), respectively.
>
> It also extends the list_lru API with a new function, list_lru_putback,
> which undoes a previous list_lru_isolate call. Unlike list_lru_add, it
> does not increment the LRU node count (as list_lru_isolate does not
> decrement the node count). list_lru_putback also allows for explicit
> memcg and NUMA node selection.
>
> Suggested-by: Johannes Weiner <[email protected]>
> Signed-off-by: Nhat Pham <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
On Mon, Nov 27, 2023 at 03:45:56PM -0800, Nhat Pham wrote:
> The new zswap writeback scheme requires an online-only memcg hierarchy
> traversal. Add this functionality via the new mem_cgroup_iter_online()
> function - the old mem_cgroup_iter() is a special case of this new
> function.
>
> Suggested-by: Andrew Morton <[email protected]>
> Signed-off-by: Nhat Pham <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
On Mon, Nov 27, 2023 at 03:45:57PM -0800, Nhat Pham wrote:
> static void shrink_worker(struct work_struct *w)
> {
> struct zswap_pool *pool = container_of(w, typeof(*pool),
> shrink_work);
> + struct mem_cgroup *memcg;
> int ret, failures = 0;
>
> + /* global reclaim will select cgroup in a round-robin fashion. */
> do {
> - ret = zswap_reclaim_entry(pool);
> - if (ret) {
> - zswap_reject_reclaim_fail++;
> - if (ret != -EAGAIN)
> - break;
> + spin_lock(&zswap_pools_lock);
> + memcg = pool->next_shrink =
> + mem_cgroup_iter_online(NULL, pool->next_shrink, NULL, true);
> +
> + /* full round trip */
> + if (!memcg) {
> + spin_unlock(&zswap_pools_lock);
> if (++failures == MAX_RECLAIM_RETRIES)
> break;
> +
> + goto resched;
> }
> +
> + /*
> + * Acquire an extra reference to the iterated memcg in case the
> + * original reference is dropped by the zswap offlining callback.
> + */
> + css_get(&memcg->css);
struct mem_cgroup isn't defined when !CONFIG_MEMCG. This needs a
mem_cgroup_get() wrapper and a dummy function for no-memcg builds.
With that fixed, though, everything else looks good to me:
Acked-by: Johannes Weiner <[email protected]>
On Mon, Nov 27, 2023 at 03:45:58PM -0800, Nhat Pham wrote:
> From: Domenico Cerasuolo <[email protected]>
>
> Since zswap now writes back pages from memcg-specific LRUs, we now need a
> new stat to show writebacks count for each memcg.
>
> Suggested-by: Nhat Pham <[email protected]>
> Signed-off-by: Domenico Cerasuolo <[email protected]>
> Signed-off-by: Nhat Pham <[email protected]>
> ---
> include/linux/vm_event_item.h | 1 +
> mm/memcontrol.c | 1 +
> mm/vmstat.c | 1 +
> mm/zswap.c | 3 +++
> 4 files changed, 6 insertions(+)
>
> diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
> index d1b847502f09..f4569ad98edf 100644
> --- a/include/linux/vm_event_item.h
> +++ b/include/linux/vm_event_item.h
> @@ -142,6 +142,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
> #ifdef CONFIG_ZSWAP
> ZSWPIN,
> ZSWPOUT,
> + ZSWP_WB,
> #endif
> #ifdef CONFIG_X86
> DIRECT_MAP_LEVEL2_SPLIT,
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 8c0f3f971179..f88c8fd03689 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -703,6 +703,7 @@ static const unsigned int memcg_vm_event_stat[] = {
> #if defined(CONFIG_MEMCG_KMEM) && defined(CONFIG_ZSWAP)
> ZSWPIN,
> ZSWPOUT,
> + ZSWP_WB,
> #endif
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> THP_FAULT_ALLOC,
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index afa5a38fcc9c..2249f85e4a87 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1401,6 +1401,7 @@ const char * const vmstat_text[] = {
> #ifdef CONFIG_ZSWAP
> "zswpin",
> "zswpout",
> + "zswp_wb",
ZSWPWB and "zswpwb" would match the existing naming scheme a bit
better.
> #endif
> #ifdef CONFIG_X86
> "direct_map_level2_splits",
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 5e397fc1f375..6a761753f979 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -754,6 +754,9 @@ static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_o
> }
> zswap_written_back_pages++;
>
> + if (entry->objcg)
> + count_objcg_event(entry->objcg, ZSWP_WB);
> +
You need to call count_vm_event() as well, otherwise the /proc/vmstat
counter will stay zero.
On Mon, Nov 27, 2023 at 03:46:00PM -0800, Nhat Pham wrote:
> Currently, we only shrink the zswap pool when the user-defined limit is
> hit. This means that if we set the limit too high, cold data that are
> unlikely to be used again will reside in the pool, wasting precious
> memory. It is hard to predict how much zswap space will be needed ahead
> of time, as this depends on the workload (specifically, on factors such
> as memory access patterns and compressibility of the memory pages).
>
> This patch implements a memcg- and NUMA-aware shrinker for zswap, that
> is initiated when there is memory pressure. The shrinker does not
> have any parameter that must be tuned by the user, and can be opted in
> or out on a per-memcg basis.
>
> Furthermore, to make it more robust for many workloads and prevent
> overshrinking (i.e evicting warm pages that might be refaulted into
> memory), we build in the following heuristics:
>
> * Estimate the number of warm pages residing in zswap, and attempt to
> protect this region of the zswap LRU.
> * Scale the number of freeable objects by an estimate of the memory
> saving factor. The better zswap compresses the data, the fewer pages
> we will evict to swap (as we will otherwise incur IO for relatively
> small memory saving).
> * During reclaim, if the shrinker encounters a page that is also being
> brought into memory, the shrinker will cautiously terminate its
> shrinking action, as this is a sign that it is touching the warmer
> region of the zswap LRU.
>
> As a proof of concept, we ran the following synthetic benchmark:
> build the linux kernel in a memory-limited cgroup, and allocate some
> cold data in tmpfs to see if the shrinker could write them out and
> improved the overall performance. Depending on the amount of cold data
> generated, we observe from 14% to 35% reduction in kernel CPU time used
> in the kernel builds.
I think this is a really important piece of functionality for zswap.
Memory compression has been around and in use for a long time, but the
question of zswap vs swap sizing has been in the room since the hybrid
mode was first proposed. Because depending on the reuse patterns,
putting zswap with a static size limit in front of an existing swap
file can be a net negative for performance as it consumes more memory.
It's great to finally see a solution to this which makes zswap *much*
more general purpose. And something that distributions might want to
turn on per default when swap is configured.
Actually to the point where I think there should be a config option to
enable the shrinker per default. Maybe not right away, but in a few
releases when this feature has racked up some more production time.
> @@ -687,6 +687,7 @@ struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
> &page_allocated, false);
> if (unlikely(page_allocated))
> swap_readpage(page, false, NULL);
> + zswap_lruvec_swapin(page);
The "lruvec" in the name vs the page parameter is a bit odd.
zswap_page_swapin() would be slightly better, but it still also sounds
like it would cause an actual swapin of some sort.
zswap_record_swapin()?
> @@ -520,6 +575,95 @@ static struct zswap_entry *zswap_entry_find_get(struct rb_root *root,
> return entry;
> }
>
> +/*********************************
> +* shrinker functions
> +**********************************/
> +static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_one *l,
> + spinlock_t *lock, void *arg);
> +
> +static unsigned long zswap_shrinker_scan(struct shrinker *shrinker,
> + struct shrink_control *sc)
> +{
> + struct lruvec *lruvec = mem_cgroup_lruvec(sc->memcg, NODE_DATA(sc->nid));
> + unsigned long shrink_ret, nr_protected, lru_size;
> + struct zswap_pool *pool = shrinker->private_data;
> + bool encountered_page_in_swapcache = false;
> +
> + nr_protected =
> + atomic_long_read(&lruvec->zswap_lruvec_state.nr_zswap_protected);
> + lru_size = list_lru_shrink_count(&pool->list_lru, sc);
> +
> + /*
> + * Abort if the shrinker is disabled or if we are shrinking into the
> + * protected region.
> + */
> + if (!zswap_shrinker_enabled || nr_protected >= lru_size - sc->nr_to_scan) {
> + sc->nr_scanned = 0;
> + return SHRINK_STOP;
> + }
I'm scratching my head at the protection check. zswap_shrinker_count()
already factors protection into account, so sc->nr_to_scan should only
be what is left on the list after excluding the protected area.
Do we even get here if the whole list is protected? Is this to protect
against concurrent shrinking of the list through multiple shrinkers or
swapins? If so, a comment would be nice :)
Otherwise, this looks great to me!
Just nitpicks, no show stoppers:
Acked-by: Johannes Weiner <[email protected]>
On Wed, Nov 29, 2023 at 10:04:05AM -0500, Johannes Weiner wrote:
> On Mon, Nov 27, 2023 at 03:45:56PM -0800, Nhat Pham wrote:
> > The new zswap writeback scheme requires an online-only memcg hierarchy
> > traversal. Add this functionality via the new mem_cgroup_iter_online()
> > function - the old mem_cgroup_iter() is a special case of this new
> > function.
> >
> > Suggested-by: Andrew Morton <[email protected]>
> > Signed-off-by: Nhat Pham <[email protected]>
>
> Acked-by: Johannes Weiner <[email protected]>
I saw Michal's reply on the other thread only after I sent this.
I agree with him it would be better to just check mem_cgroup_online()
in the shinker callsite and leave mem_cgroup_iter() as-is. If it's
offline, just continue to the next mem_cgroup_iter() invocation.
On Wed, Nov 29, 2023 at 8:21 AM Johannes Weiner <[email protected]> wrote:
>
> On Mon, Nov 27, 2023 at 03:46:00PM -0800, Nhat Pham wrote:
> > Currently, we only shrink the zswap pool when the user-defined limit is
> > hit. This means that if we set the limit too high, cold data that are
> > unlikely to be used again will reside in the pool, wasting precious
> > memory. It is hard to predict how much zswap space will be needed ahead
> > of time, as this depends on the workload (specifically, on factors such
> > as memory access patterns and compressibility of the memory pages).
> >
> > This patch implements a memcg- and NUMA-aware shrinker for zswap, that
> > is initiated when there is memory pressure. The shrinker does not
> > have any parameter that must be tuned by the user, and can be opted in
> > or out on a per-memcg basis.
> >
> > Furthermore, to make it more robust for many workloads and prevent
> > overshrinking (i.e evicting warm pages that might be refaulted into
> > memory), we build in the following heuristics:
> >
> > * Estimate the number of warm pages residing in zswap, and attempt to
> > protect this region of the zswap LRU.
> > * Scale the number of freeable objects by an estimate of the memory
> > saving factor. The better zswap compresses the data, the fewer pages
> > we will evict to swap (as we will otherwise incur IO for relatively
> > small memory saving).
> > * During reclaim, if the shrinker encounters a page that is also being
> > brought into memory, the shrinker will cautiously terminate its
> > shrinking action, as this is a sign that it is touching the warmer
> > region of the zswap LRU.
> >
> > As a proof of concept, we ran the following synthetic benchmark:
> > build the linux kernel in a memory-limited cgroup, and allocate some
> > cold data in tmpfs to see if the shrinker could write them out and
> > improved the overall performance. Depending on the amount of cold data
> > generated, we observe from 14% to 35% reduction in kernel CPU time used
> > in the kernel builds.
>
> I think this is a really important piece of functionality for zswap.
>
> Memory compression has been around and in use for a long time, but the
> question of zswap vs swap sizing has been in the room since the hybrid
> mode was first proposed. Because depending on the reuse patterns,
> putting zswap with a static size limit in front of an existing swap
> file can be a net negative for performance as it consumes more memory.
>
> It's great to finally see a solution to this which makes zswap *much*
> more general purpose. And something that distributions might want to
> turn on per default when swap is configured.
>
> Actually to the point where I think there should be a config option to
> enable the shrinker per default. Maybe not right away, but in a few
> releases when this feature has racked up some more production time.
Sure thingy - how does everyone feel about this?
>
> > @@ -687,6 +687,7 @@ struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
> > &page_allocated, false);
> > if (unlikely(page_allocated))
> > swap_readpage(page, false, NULL);
> > + zswap_lruvec_swapin(page);
>
> The "lruvec" in the name vs the page parameter is a bit odd.
> zswap_page_swapin() would be slightly better, but it still also sounds
> like it would cause an actual swapin of some sort.
>
> zswap_record_swapin()?
Hmm that sounds good to me. I'm not very good with naming, if that's
not already evident :)
>
> > @@ -520,6 +575,95 @@ static struct zswap_entry *zswap_entry_find_get(struct rb_root *root,
> > return entry;
> > }
> >
> > +/*********************************
> > +* shrinker functions
> > +**********************************/
> > +static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_one *l,
> > + spinlock_t *lock, void *arg);
> > +
> > +static unsigned long zswap_shrinker_scan(struct shrinker *shrinker,
> > + struct shrink_control *sc)
> > +{
> > + struct lruvec *lruvec = mem_cgroup_lruvec(sc->memcg, NODE_DATA(sc->nid));
> > + unsigned long shrink_ret, nr_protected, lru_size;
> > + struct zswap_pool *pool = shrinker->private_data;
> > + bool encountered_page_in_swapcache = false;
> > +
> > + nr_protected =
> > + atomic_long_read(&lruvec->zswap_lruvec_state.nr_zswap_protected);
> > + lru_size = list_lru_shrink_count(&pool->list_lru, sc);
> > +
> > + /*
> > + * Abort if the shrinker is disabled or if we are shrinking into the
> > + * protected region.
> > + */
> > + if (!zswap_shrinker_enabled || nr_protected >= lru_size - sc->nr_to_scan) {
> > + sc->nr_scanned = 0;
> > + return SHRINK_STOP;
> > + }
>
> I'm scratching my head at the protection check. zswap_shrinker_count()
> already factors protection into account, so sc->nr_to_scan should only
> be what is left on the list after excluding the protected area.
>
> Do we even get here if the whole list is protected? Is this to protect
> against concurrent shrinking of the list through multiple shrinkers or
> swapins? If so, a comment would be nice :)
Yep, this is mostly for concurrent shrinkers. Please fact-check me,
but IIUC if we have too many reclaimers all calling upon the zswap
shrinker (before any of them can make substantial progress), we can
have a situation where the total number of objects freed by the
reclaimers will eat into the protection area of the zswap LRU (even if
the number of freeable objects is scaled down by the compression
ratio, and further scaled down internally in the shrinker/vmscan
code). I've observed this tendency when there is a) a lot of worker
threads in my benchmark and b) memory pressure. This is a crude/racy
way to alleviate the issue.
I think this is actually a wider problem than just zswap and zswap
shrinker - we need better reclaimer throttling logic IMO. Perhaps this
check should be done higher up the stack - something along the lines
of having each reclaimer "register" its intention (number of objects
it wants to reclaim) to a particular shrinker, allowing the shrinker
to deny a reclaimer if there is already a strong reclaim driving
force. Or some other throttling heuristics based on the number of
freeable objects and the reclaimer registration data.
>
> Otherwise, this looks great to me!
>
> Just nitpicks, no show stoppers:
>
> Acked-by: Johannes Weiner <[email protected]>
On Wed, Nov 29, 2023 at 7:17 AM Johannes Weiner <[email protected]> wrote:
>
> On Mon, Nov 27, 2023 at 03:45:57PM -0800, Nhat Pham wrote:
> > static void shrink_worker(struct work_struct *w)
> > {
> > struct zswap_pool *pool = container_of(w, typeof(*pool),
> > shrink_work);
> > + struct mem_cgroup *memcg;
> > int ret, failures = 0;
> >
> > + /* global reclaim will select cgroup in a round-robin fashion. */
> > do {
> > - ret = zswap_reclaim_entry(pool);
> > - if (ret) {
> > - zswap_reject_reclaim_fail++;
> > - if (ret != -EAGAIN)
> > - break;
> > + spin_lock(&zswap_pools_lock);
> > + memcg = pool->next_shrink =
> > + mem_cgroup_iter_online(NULL, pool->next_shrink, NULL, true);
> > +
> > + /* full round trip */
> > + if (!memcg) {
> > + spin_unlock(&zswap_pools_lock);
> > if (++failures == MAX_RECLAIM_RETRIES)
> > break;
> > +
> > + goto resched;
> > }
> > +
> > + /*
> > + * Acquire an extra reference to the iterated memcg in case the
> > + * original reference is dropped by the zswap offlining callback.
> > + */
> > + css_get(&memcg->css);
>
> struct mem_cgroup isn't defined when !CONFIG_MEMCG. This needs a
> mem_cgroup_get() wrapper and a dummy function for no-memcg builds.
I got this exact same issue a couple of versions ago, but it was
hidden behind another helper function which can be implemented as a
no-op in the case of !CONFIG_MEMCG, so I forgot about it until now. It
always strikes me a bit weird that we have mem_cgroup_put() but not an
equivalent get - let me correct that.
>
> With that fixed, though, everything else looks good to me:
>
> Acked-by: Johannes Weiner <[email protected]>
Thanks for the review, Johannes!
On Wed, Nov 29, 2023 at 4:21 PM Nhat Pham <[email protected]> wrote:
>
> On Wed, Nov 29, 2023 at 7:17 AM Johannes Weiner <[email protected]> wrote:
> >
> > On Mon, Nov 27, 2023 at 03:45:57PM -0800, Nhat Pham wrote:
> > > static void shrink_worker(struct work_struct *w)
> > > {
> > > struct zswap_pool *pool = container_of(w, typeof(*pool),
> > > shrink_work);
> > > + struct mem_cgroup *memcg;
> > > int ret, failures = 0;
> > >
> > > + /* global reclaim will select cgroup in a round-robin fashion. */
> > > do {
> > > - ret = zswap_reclaim_entry(pool);
> > > - if (ret) {
> > > - zswap_reject_reclaim_fail++;
> > > - if (ret != -EAGAIN)
> > > - break;
> > > + spin_lock(&zswap_pools_lock);
> > > + memcg = pool->next_shrink =
> > > + mem_cgroup_iter_online(NULL, pool->next_shrink, NULL, true);
> > > +
> > > + /* full round trip */
> > > + if (!memcg) {
> > > + spin_unlock(&zswap_pools_lock);
> > > if (++failures == MAX_RECLAIM_RETRIES)
> > > break;
> > > +
> > > + goto resched;
> > > }
> > > +
> > > + /*
> > > + * Acquire an extra reference to the iterated memcg in case the
> > > + * original reference is dropped by the zswap offlining callback.
> > > + */
> > > + css_get(&memcg->css);
> >
> > struct mem_cgroup isn't defined when !CONFIG_MEMCG. This needs a
> > mem_cgroup_get() wrapper and a dummy function for no-memcg builds.
>
> I got this exact same issue a couple of versions ago, but it was
> hidden behind another helper function which can be implemented as a
> no-op in the case of !CONFIG_MEMCG, so I forgot about it until now. It
> always strikes me a bit weird that we have mem_cgroup_put() but not an
> equivalent get - let me correct that.
Actually, I'll instead implement mem_cgroup_tryget_online(), as we
have to check for the cgroup's onlineness as well anyway! If it's
online, then keep the extra reference - all good. If it's not, then
drop the original reference before releasing the lock.
>
> >
> > With that fixed, though, everything else looks good to me:
> >
> > Acked-by: Johannes Weiner <[email protected]>
>
> Thanks for the review, Johannes!
On Wed, Nov 29, 2023 at 7:25 AM Johannes Weiner <[email protected]> wrote:
>
> On Mon, Nov 27, 2023 at 03:45:58PM -0800, Nhat Pham wrote:
> > From: Domenico Cerasuolo <[email protected]>
> >
> > Since zswap now writes back pages from memcg-specific LRUs, we now need a
> > new stat to show writebacks count for each memcg.
> >
> > Suggested-by: Nhat Pham <[email protected]>
> > Signed-off-by: Domenico Cerasuolo <[email protected]>
> > Signed-off-by: Nhat Pham <[email protected]>
> > ---
> > include/linux/vm_event_item.h | 1 +
> > mm/memcontrol.c | 1 +
> > mm/vmstat.c | 1 +
> > mm/zswap.c | 3 +++
> > 4 files changed, 6 insertions(+)
> >
> > diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
> > index d1b847502f09..f4569ad98edf 100644
> > --- a/include/linux/vm_event_item.h
> > +++ b/include/linux/vm_event_item.h
> > @@ -142,6 +142,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
> > #ifdef CONFIG_ZSWAP
> > ZSWPIN,
> > ZSWPOUT,
> > + ZSWP_WB,
> > #endif
> > #ifdef CONFIG_X86
> > DIRECT_MAP_LEVEL2_SPLIT,
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index 8c0f3f971179..f88c8fd03689 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -703,6 +703,7 @@ static const unsigned int memcg_vm_event_stat[] = {
> > #if defined(CONFIG_MEMCG_KMEM) && defined(CONFIG_ZSWAP)
> > ZSWPIN,
> > ZSWPOUT,
> > + ZSWP_WB,
> > #endif
> > #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > THP_FAULT_ALLOC,
> > diff --git a/mm/vmstat.c b/mm/vmstat.c
> > index afa5a38fcc9c..2249f85e4a87 100644
> > --- a/mm/vmstat.c
> > +++ b/mm/vmstat.c
> > @@ -1401,6 +1401,7 @@ const char * const vmstat_text[] = {
> > #ifdef CONFIG_ZSWAP
> > "zswpin",
> > "zswpout",
> > + "zswp_wb",
>
> ZSWPWB and "zswpwb" would match the existing naming scheme a bit
> better.
>
> > #endif
> > #ifdef CONFIG_X86
> > "direct_map_level2_splits",
> > diff --git a/mm/zswap.c b/mm/zswap.c
> > index 5e397fc1f375..6a761753f979 100644
> > --- a/mm/zswap.c
> > +++ b/mm/zswap.c
> > @@ -754,6 +754,9 @@ static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_o
> > }
> > zswap_written_back_pages++;
> >
> > + if (entry->objcg)
> > + count_objcg_event(entry->objcg, ZSWP_WB);
> > +
>
> You need to call count_vm_event() as well, otherwise the /proc/vmstat
> counter will stay zero.
Ahh I didn't check that. I only looked at the cgroup's memory.stat
counter. I'll fix this for v8!
On Mon, Nov 27, 2023 at 03:45:54PM -0800, Nhat Pham wrote:
> Changelog:
> v7:
> * Added the mem_cgroup_iter_online() function to the API for the new
> behavior (suggested by Andrew Morton) (patch 2)
> * Fixed a missing list_lru_del -> list_lru_del_obj (patch 1)
> v6:
> * Rebase on top of latest mm-unstable.
> * Fix/improve the in-code documentation of the new list_lru
> manipulation functions (patch 1)
> v5:
> * Replace reference getting with an rcu_read_lock() section for
> zswap lru modifications (suggested by Yosry)
> * Add a new prep patch that allows mem_cgroup_iter() to return
> online cgroup.
> * Add a callback that updates pool->next_shrink when the cgroup is
> offlined (suggested by Yosry Ahmed, Johannes Weiner)
> v4:
> * Rename list_lru_add to list_lru_add_obj and __list_lru_add to
> list_lru_add (patch 1) (suggested by Johannes Weiner and
> Yosry Ahmed)
> * Some cleanups on the memcg aware LRU patch (patch 2)
> (suggested by Yosry Ahmed)
> * Use event interface for the new per-cgroup writeback counters.
> (patch 3) (suggested by Yosry Ahmed)
> * Abstract zswap's lruvec states and handling into
> zswap_lruvec_state (patch 5) (suggested by Yosry Ahmed)
> v3:
> * Add a patch to export per-cgroup zswap writeback counters
> * Add a patch to update zswap's kselftest
> * Separate the new list_lru functions into its own prep patch
> * Do not start from the top of the hierarchy when encounter a memcg
> that is not online for the global limit zswap writeback (patch 2)
> (suggested by Yosry Ahmed)
> * Do not remove the swap entry from list_lru in
> __read_swapcache_async() (patch 2) (suggested by Yosry Ahmed)
> * Removed a redundant zswap pool getting (patch 2)
> (reported by Ryan Roberts)
> * Use atomic for the nr_zswap_protected (instead of lruvec's lock)
> (patch 5) (suggested by Yosry Ahmed)
> * Remove the per-cgroup zswap shrinker knob (patch 5)
> (suggested by Yosry Ahmed)
> v2:
> * Fix loongarch compiler errors
> * Use pool stats instead of memcg stats when !CONFIG_MEMCG_KEM
>
> There are currently several issues with zswap writeback:
>
> 1. There is only a single global LRU for zswap, making it impossible to
> perform worload-specific shrinking - an memcg under memory pressure
> cannot determine which pages in the pool it owns, and often ends up
> writing pages from other memcgs. This issue has been previously
> observed in practice and mitigated by simply disabling
> memcg-initiated shrinking:
>
> https://lore.kernel.org/all/[email protected]/T/#u
>
> But this solution leaves a lot to be desired, as we still do not
> have an avenue for an memcg to free up its own memory locked up in
> the zswap pool.
>
> 2. We only shrink the zswap pool when the user-defined limit is hit.
> This means that if we set the limit too high, cold data that are
> unlikely to be used again will reside in the pool, wasting precious
> memory. It is hard to predict how much zswap space will be needed
> ahead of time, as this depends on the workload (specifically, on
> factors such as memory access patterns and compressibility of the
> memory pages).
>
> This patch series solves these issues by separating the global zswap
> LRU into per-memcg and per-NUMA LRUs, and performs workload-specific
> (i.e memcg- and NUMA-aware) zswap writeback under memory pressure. The
> new shrinker does not have any parameter that must be tuned by the
> user, and can be opted in or out on a per-memcg basis.
>
> As a proof of concept, we ran the following synthetic benchmark:
> build the linux kernel in a memory-limited cgroup, and allocate some
> cold data in tmpfs to see if the shrinker could write them out and
> improved the overall performance. Depending on the amount of cold data
> generated, we observe from 14% to 35% reduction in kernel CPU time used
> in the kernel builds.
>
> Domenico Cerasuolo (3):
> zswap: make shrinking memcg-aware
> mm: memcg: add per-memcg zswap writeback stat
> selftests: cgroup: update per-memcg zswap writeback selftest
>
> Nhat Pham (3):
> list_lru: allows explicit memcg and NUMA node selection
> memcontrol: add a new function to traverse online-only memcg hierarchy
> zswap: shrinks zswap pool based on memory pressure
>
> Documentation/admin-guide/mm/zswap.rst | 7 +
> drivers/android/binder_alloc.c | 7 +-
> fs/dcache.c | 8 +-
> fs/gfs2/quota.c | 6 +-
> fs/inode.c | 4 +-
> fs/nfs/nfs42xattr.c | 8 +-
> fs/nfsd/filecache.c | 4 +-
> fs/xfs/xfs_buf.c | 6 +-
> fs/xfs/xfs_dquot.c | 2 +-
> fs/xfs/xfs_qm.c | 2 +-
> include/linux/list_lru.h | 54 ++-
> include/linux/memcontrol.h | 18 +
> include/linux/mmzone.h | 2 +
> include/linux/vm_event_item.h | 1 +
> include/linux/zswap.h | 27 +-
> mm/list_lru.c | 48 ++-
> mm/memcontrol.c | 32 +-
> mm/mmzone.c | 1 +
> mm/swap.h | 3 +-
> mm/swap_state.c | 26 +-
> mm/vmstat.c | 1 +
> mm/workingset.c | 4 +-
> mm/zswap.c | 426 +++++++++++++++++---
> tools/testing/selftests/cgroup/test_zswap.c | 74 ++--
> 24 files changed, 641 insertions(+), 130 deletions(-)
>
>
> base-commit: 5cdba94229e58a39ca389ad99763af29e6b0c5a5
No regressions when booting kernel with series applied.
Tested-by: Bagas Sanjaya <[email protected]>
--
An old man doll... just what I always wanted! - Clara