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Date:   Wed,  1 May 2019 18:42:16 -0700
Message-Id: <20190502014216.225568-1-drosen@google.com>
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Subject: [PATCH v2] f2fs: Add option to limit required GC for checkpoint=disable
From:   Daniel Rosenberg <drosen@google.com>
To:     Jaegeuk Kim <jaegeuk@kernel.org>, Chao Yu <yuchao0@huawei.com>,
        Jonathan Corbet <corbet@lwn.net>,
        linux-f2fs-devel@lists.sourceforge.net
Cc:     linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, kernel-team@android.com,
        Daniel Rosenberg <drosen@google.com>
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Sender: linux-kernel-owner@vger.kernel.org
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This extends the checkpoint option to allow checkpoint=disable:%u
This allows you to specify what percent of the drive you are willing
to lose access to while mounting with checkpoint=disable. If the amount
lost would be higher, the mount will return -EAGAIN.
Currently, we need to run garbage collection until the amount of holes
is smaller than the OVP space. With the new option, f2fs can mark
space as unusable up front instead of requiring that
the space be freed up with garbage collection.

Change-Id: Ib8c3cb46085bf4aac3cdc06d4b64d6a20db87028
Signed-off-by: Daniel Rosenberg <drosen@google.com>
---

> If we allow a high unusable blocks, I doubt in inc_valid_{node,block}_count(),
> we may overflow in below calculation:
> 
>         if (unlikely(is_sbi_flag_set(sbi, SBI_CP_DISABLED)))
>                 valid_block_count += sbi->unusable_block_count;
> 
>         if (unlikely(is_sbi_flag_set(sbi, SBI_CP_DISABLED)))
>                 avail_user_block_count -= sbi->unusable_block_count;
The starting value of unusable_block_count is limited.
Considering the case where the disk is full, we have
total blocks = used + OVP
OVP = reserved + holes
So, the holes must be less than OVP, and unusable = 0

In general, total = used + available + OVP
total-used-OVP=avail

(free being blocks from free segments,
available being blocks available to the user)
reserved + holes + free = OVP + available
holes - OVP = available - reserved - free

unusable = max(data_holes, node_holes)-OVP
unusable <= holes-OVP

unusable <= available-reserved - free segs
unusable <= available

similarly,
total = used + available + OVP
reserved + holes + free = OVP + available
available = reserved + holes + free - OVP
total = used + reserved + holes + free - OVP
unusable<=holes-OVP
total >= used + reserved + unusable + free
total >= used + unusable

So the unusable block count is lower than the available block count when we
first mount with checkpoint=disable, and we only grow unusable when we grow
available blocks. We also have an upper bound on used+unusable which is less
the total block count. So unless I've missed something elsewhere, we should
not be able to underflow or overflow these values.

v2:
Changed default to 0 to be in line with current behavior.
Adjusted description of checkpoint=disable to be more clear, since with that
default, mounting with checkpoint=disable may return EAGAIN unless you use
checkpoint=disable:100
Changed description of /sys/fs/f2fs/<disk>/unusable to be clearer

 Documentation/ABI/testing/sysfs-fs-f2fs |  8 +++++
 Documentation/filesystems/f2fs.txt      | 12 ++++++-
 fs/f2fs/f2fs.h                          |  6 +++-
 fs/f2fs/segment.c                       | 17 ++++++++--
 fs/f2fs/super.c                         | 44 +++++++++++++------------
 fs/f2fs/sysfs.c                         | 16 +++++++++
 6 files changed, 77 insertions(+), 26 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-fs-f2fs b/Documentation/ABI/testing/sysfs-fs-f2fs
index 91822ce258317..dca326e0ee3e1 100644
--- a/Documentation/ABI/testing/sysfs-fs-f2fs
+++ b/Documentation/ABI/testing/sysfs-fs-f2fs
@@ -243,3 +243,11 @@ Description:
 		 - Del: echo '[h/c]!extension' > /sys/fs/f2fs/<disk>/extension_list
 		 - [h] means add/del hot file extension
 		 - [c] means add/del cold file extension
+
+What:		/sys/fs/f2fs/<disk>/unusable
+Date		April 2019
+Contact:	"Daniel Rosenberg" <drosen@google.com>
+Description:
+		If checkpoint=disable, it displays the number of blocks that are unusable.
+                If checkpoint=enable it displays the enumber of blocks that would be unusable
+                if checkpoint=disable were to be set.
diff --git a/Documentation/filesystems/f2fs.txt b/Documentation/filesystems/f2fs.txt
index f7b5e4ff0de3e..d49f5ac8bf9b6 100644
--- a/Documentation/filesystems/f2fs.txt
+++ b/Documentation/filesystems/f2fs.txt
@@ -214,11 +214,21 @@ fsync_mode=%s          Control the policy of fsync. Currently supports "posix",
                        non-atomic files likewise "nobarrier" mount option.
 test_dummy_encryption  Enable dummy encryption, which provides a fake fscrypt
                        context. The fake fscrypt context is used by xfstests.
-checkpoint=%s          Set to "disable" to turn off checkpointing. Set to "enable"
+checkpoint=%s[:%u]     Set to "disable" to turn off checkpointing. Set to "enable"
                        to reenable checkpointing. Is enabled by default. While
                        disabled, any unmounting or unexpected shutdowns will cause
                        the filesystem contents to appear as they did when the
                        filesystem was mounted with that option.
+                       While mounting with checkpoint=disabled, the filesystem must
+                       run garbage collection to ensure that all available space can
+                       be used. If this takes too much time, the mount may return
+                       EAGAIN. You may optionally add a percentage to indicate what
+                       percent of the disk you would be willing to temporarily give
+                       up to avoid additional garbage collection. For instance,
+                       checkpoint=disable:100 would always succeed, but would
+                       potentially make the disk appear full. The actual space that
+                       would be unsuable can be viewed at /sys/fs/f2fs/<disk>/unusable
+                       This space is reclaimed once checkpoint=enable.
 
 ================================================================================
 DEBUGFS ENTRIES
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 30acde08822ef..d0477251cec56 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -136,6 +136,9 @@ struct f2fs_mount_info {
 	int alloc_mode;			/* segment allocation policy */
 	int fsync_mode;			/* fsync policy */
 	bool test_dummy_encryption;	/* test dummy encryption */
+	block_t unusable_percent_cap;   /* Percent of space allowed to be
+					 * unusable when disabling checkpoint
+					 */
 };
 
 #define F2FS_FEATURE_ENCRYPT		0x0001
@@ -3049,7 +3052,8 @@ bool f2fs_issue_discard_timeout(struct f2fs_sb_info *sbi);
 void f2fs_clear_prefree_segments(struct f2fs_sb_info *sbi,
 					struct cp_control *cpc);
 void f2fs_dirty_to_prefree(struct f2fs_sb_info *sbi);
-int f2fs_disable_cp_again(struct f2fs_sb_info *sbi);
+block_t f2fs_get_unusable_blocks(struct f2fs_sb_info *sbi);
+int f2fs_disable_cp_again(struct f2fs_sb_info *sbi, block_t unusable);
 void f2fs_release_discard_addrs(struct f2fs_sb_info *sbi);
 int f2fs_npages_for_summary_flush(struct f2fs_sb_info *sbi, bool for_ra);
 void f2fs_allocate_new_segments(struct f2fs_sb_info *sbi);
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index a3380d1de6000..704224f4a2866 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -869,11 +869,12 @@ void f2fs_dirty_to_prefree(struct f2fs_sb_info *sbi)
 	mutex_unlock(&dirty_i->seglist_lock);
 }
 
-int f2fs_disable_cp_again(struct f2fs_sb_info *sbi)
+block_t f2fs_get_unusable_blocks(struct f2fs_sb_info *sbi)
 {
-	struct dirty_seglist_info *dirty_i = DIRTY_I(sbi);
 	block_t ovp = overprovision_segments(sbi) << sbi->log_blocks_per_seg;
+	struct dirty_seglist_info *dirty_i = DIRTY_I(sbi);
 	block_t holes[2] = {0, 0};	/* DATA and NODE */
+	block_t unusable;
 	struct seg_entry *se;
 	unsigned int segno;
 
@@ -887,7 +888,17 @@ int f2fs_disable_cp_again(struct f2fs_sb_info *sbi)
 	}
 	mutex_unlock(&dirty_i->seglist_lock);
 
-	if (holes[DATA] > ovp || holes[NODE] > ovp)
+	unusable = holes[DATA] > holes[NODE] ? holes[DATA] : holes[NODE];
+	if (unusable > ovp)
+		return unusable - ovp;
+	return 0;
+}
+
+int f2fs_disable_cp_again(struct f2fs_sb_info *sbi, block_t unusable)
+{
+	block_t max_allowed =  (sbi->user_block_count / 100) *
+			F2FS_OPTION(sbi).unusable_percent_cap;
+	if (unusable > max_allowed)
 		return -EAGAIN;
 	if (is_sbi_flag_set(sbi, SBI_CP_DISABLED_QUICK) &&
 		dirty_segments(sbi) > overprovision_segments(sbi))
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 0b6fa77c35f3e..640753cb3f73f 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -136,7 +136,9 @@ enum {
 	Opt_alloc,
 	Opt_fsync,
 	Opt_test_dummy_encryption,
-	Opt_checkpoint,
+	Opt_checkpoint_disable,
+	Opt_checkpoint_disable_cap,
+	Opt_checkpoint_enable,
 	Opt_err,
 };
 
@@ -195,7 +197,9 @@ static match_table_t f2fs_tokens = {
 	{Opt_alloc, "alloc_mode=%s"},
 	{Opt_fsync, "fsync_mode=%s"},
 	{Opt_test_dummy_encryption, "test_dummy_encryption"},
-	{Opt_checkpoint, "checkpoint=%s"},
+	{Opt_checkpoint_disable, "checkpoint=disable"},
+	{Opt_checkpoint_disable_cap, "checkpoint=disable:%u"},
+	{Opt_checkpoint_enable, "checkpoint=enable"},
 	{Opt_err, NULL},
 };
 
@@ -771,22 +775,17 @@ static int parse_options(struct super_block *sb, char *options)
 					"Test dummy encryption mount option ignored");
 #endif
 			break;
-		case Opt_checkpoint:
-			name = match_strdup(&args[0]);
-			if (!name)
-				return -ENOMEM;
-
-			if (strlen(name) == 6 &&
-					!strncmp(name, "enable", 6)) {
-				clear_opt(sbi, DISABLE_CHECKPOINT);
-			} else if (strlen(name) == 7 &&
-					!strncmp(name, "disable", 7)) {
-				set_opt(sbi, DISABLE_CHECKPOINT);
-			} else {
-				kvfree(name);
+		case Opt_checkpoint_disable_cap:
+			if (args->from && match_int(args, &arg))
 				return -EINVAL;
-			}
-			kvfree(name);
+			if (arg < 0 || arg > 100)
+				return -EINVAL;
+			F2FS_OPTION(sbi).unusable_percent_cap = arg;
+		case Opt_checkpoint_disable:
+			set_opt(sbi, DISABLE_CHECKPOINT);
+			break;
+		case Opt_checkpoint_enable:
+			clear_opt(sbi, DISABLE_CHECKPOINT);
 			break;
 		default:
 			f2fs_msg(sb, KERN_ERR,
@@ -1411,8 +1410,8 @@ static int f2fs_show_options(struct seq_file *seq, struct dentry *root)
 		seq_printf(seq, ",alloc_mode=%s", "reuse");
 
 	if (test_opt(sbi, DISABLE_CHECKPOINT))
-		seq_puts(seq, ",checkpoint=disable");
-
+		seq_printf(seq, ",checkpoint=disable:%u",
+				F2FS_OPTION(sbi).unusable_percent_cap);
 	if (F2FS_OPTION(sbi).fsync_mode == FSYNC_MODE_POSIX)
 		seq_printf(seq, ",fsync_mode=%s", "posix");
 	else if (F2FS_OPTION(sbi).fsync_mode == FSYNC_MODE_STRICT)
@@ -1441,6 +1440,7 @@ static void default_options(struct f2fs_sb_info *sbi)
 	set_opt(sbi, EXTENT_CACHE);
 	set_opt(sbi, NOHEAP);
 	clear_opt(sbi, DISABLE_CHECKPOINT);
+	F2FS_OPTION(sbi).unusable_percent_cap = 0;
 	sbi->sb->s_flags |= SB_LAZYTIME;
 	set_opt(sbi, FLUSH_MERGE);
 	set_opt(sbi, DISCARD);
@@ -1469,6 +1469,7 @@ static int f2fs_disable_checkpoint(struct f2fs_sb_info *sbi)
 	struct cp_control cpc;
 	int err = 0;
 	int ret;
+	block_t unusable;
 
 	if (s_flags & SB_RDONLY) {
 		f2fs_msg(sbi->sb, KERN_ERR,
@@ -1496,7 +1497,8 @@ static int f2fs_disable_checkpoint(struct f2fs_sb_info *sbi)
 		goto restore_flag;
 	}
 
-	if (f2fs_disable_cp_again(sbi)) {
+	unusable = f2fs_get_unusable_blocks(sbi);
+	if (f2fs_disable_cp_again(sbi, unusable)) {
 		err = -EAGAIN;
 		goto restore_flag;
 	}
@@ -1506,7 +1508,7 @@ static int f2fs_disable_checkpoint(struct f2fs_sb_info *sbi)
 	set_sbi_flag(sbi, SBI_CP_DISABLED);
 	f2fs_write_checkpoint(sbi, &cpc);
 
-	sbi->unusable_block_count = 0;
+	sbi->unusable_block_count = unusable;
 	mutex_unlock(&sbi->gc_mutex);
 restore_flag:
 	sbi->sb->s_flags = s_flags;	/* Restore MS_RDONLY status */
diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
index 729f46a3c9ee0..fa184880cff34 100644
--- a/fs/f2fs/sysfs.c
+++ b/fs/f2fs/sysfs.c
@@ -68,6 +68,20 @@ static ssize_t dirty_segments_show(struct f2fs_attr *a,
 		(unsigned long long)(dirty_segments(sbi)));
 }
 
+static ssize_t unusable_show(struct f2fs_attr *a,
+		struct f2fs_sb_info *sbi, char *buf)
+{
+	block_t unusable;
+
+	if (test_opt(sbi, DISABLE_CHECKPOINT))
+		unusable = sbi->unusable_block_count;
+	else
+		unusable = f2fs_get_unusable_blocks(sbi);
+	return snprintf(buf, PAGE_SIZE, "%llu\n",
+		(unsigned long long)unusable);
+}
+
+
 static ssize_t lifetime_write_kbytes_show(struct f2fs_attr *a,
 		struct f2fs_sb_info *sbi, char *buf)
 {
@@ -440,6 +454,7 @@ F2FS_GENERAL_RO_ATTR(dirty_segments);
 F2FS_GENERAL_RO_ATTR(lifetime_write_kbytes);
 F2FS_GENERAL_RO_ATTR(features);
 F2FS_GENERAL_RO_ATTR(current_reserved_blocks);
+F2FS_GENERAL_RO_ATTR(unusable);
 
 #ifdef CONFIG_FS_ENCRYPTION
 F2FS_FEATURE_RO_ATTR(encryption, FEAT_CRYPTO);
@@ -495,6 +510,7 @@ static struct attribute *f2fs_attrs[] = {
 	ATTR_LIST(inject_type),
 #endif
 	ATTR_LIST(dirty_segments),
+	ATTR_LIST(unusable),
 	ATTR_LIST(lifetime_write_kbytes),
 	ATTR_LIST(features),
 	ATTR_LIST(reserved_blocks),
-- 
2.21.0.593.g511ec345e18-goog