[f2fs-dev] [PATCH v3] f2fs: introduce flush_policy sysfs entry

[Chao Yu via Linux-f2fs-devel <linux-f2fs-devel@lists.sourceforge.net>]

This patch introduces a new sysfs entry /sys/fs/f2fs/<disk>/flush_policy
in order to tune performance of f2fs data flush flow.

For example, checkpoint will use REQ_FUA to persist CP metadata, however,
some kind device has bad performance on REQ_FUA command, result in that
checkpoint being blocked for long time, w/ this sysfs entry, we can give
an option to use REQ_PREFLUSH command instead of REQ_FUA during checkpoint,
it can help to mitigate long latency of checkpoint.

Signed-off-by: Chao Yu <chao@kernel.org>
---
v3:
- export f2fs_submit_flush_wait()
 Documentation/ABI/testing/sysfs-fs-f2fs |  9 +++++++++
 fs/f2fs/checkpoint.c                    | 11 ++++++++++-
 fs/f2fs/f2fs.h                          |  9 +++++++++
 fs/f2fs/segment.c                       |  8 ++++----
 fs/f2fs/sysfs.c                         |  9 +++++++++
 5 files changed, 41 insertions(+), 5 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-fs-f2fs b/Documentation/ABI/testing/sysfs-fs-f2fs
index bc0e7fefc39d..2fedb44b713b 100644
--- a/Documentation/ABI/testing/sysfs-fs-f2fs
+++ b/Documentation/ABI/testing/sysfs-fs-f2fs
@@ -883,3 +883,12 @@ Date:		June 2025
 Contact:	"Daeho Jeong" <daehojeong@google.com>
 Description:	Control GC algorithm for boost GC. 0: cost benefit, 1: greedy
 		Default: 1
+
+What:		/sys/fs/f2fs/<disk>/flush_policy
+Date:		July 2025
+Contact:	"Chao Yu" <chao@kernel.org>
+Description:	Device has different performance for the same flush methods, this node
+		can be used to tune performance by setting different flush methods.
+
+		policy value		description
+		0x00000001		Use preflush instead of fua during checkpoint
diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
index db3831f7f2f5..2450e382fe6b 100644
--- a/fs/f2fs/checkpoint.c
+++ b/fs/f2fs/checkpoint.c
@@ -1419,7 +1419,9 @@ static void commit_checkpoint(struct f2fs_sb_info *sbi,
 	f2fs_folio_put(folio, false);
 
 	/* submit checkpoint (with barrier if NOBARRIER is not set) */
-	f2fs_submit_merged_write(sbi, META_FLUSH);
+	f2fs_submit_merged_write(sbi,
+		sbi->flush_policy & BIT(FLUSH_POLICY_CP_NO_FUA) ?
+		META : META_FLUSH);
 }
 
 static inline u64 get_sectors_written(struct block_device *bdev)
@@ -1594,6 +1596,13 @@ static int do_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc)
 
 	__set_cp_next_pack(sbi);
 
+	/* flush device cache to make sure last cp pack can be persisted */
+	if (sbi->flush_policy & BIT(FLUSH_POLICY_CP_NO_FUA)) {
+		err = f2fs_submit_flush_wait(sbi, sbi->sb->s_bdev);
+		if (err)
+			return err;
+	}
+
 	/*
 	 * redirty superblock if metadata like node page or inode cache is
 	 * updated during writing checkpoint.
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 46be7560548c..e7b866a98c92 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -1594,6 +1594,11 @@ struct decompress_io_ctx {
 #define MAX_COMPRESS_LOG_SIZE		8
 #define MAX_COMPRESS_WINDOW_SIZE(log_size)	((PAGE_SIZE) << (log_size))
 
+enum flush_policy {
+	FLUSH_POLICY_CP_NO_FUA,
+	FLUSH_POLICY_MAX,
+};
+
 struct f2fs_sb_info {
 	struct super_block *sb;			/* pointer to VFS super block */
 	struct proc_dir_entry *s_proc;		/* proc entry */
@@ -1845,6 +1850,8 @@ struct f2fs_sb_info {
 	/* carve out reserved_blocks from total blocks */
 	bool carve_out;
 
+	unsigned int flush_policy;		/* flush policy */
+
 #ifdef CONFIG_F2FS_FS_COMPRESSION
 	struct kmem_cache *page_array_slab;	/* page array entry */
 	unsigned int page_array_slab_size;	/* default page array slab size */
@@ -3821,6 +3828,8 @@ int f2fs_commit_atomic_write(struct inode *inode);
 void f2fs_abort_atomic_write(struct inode *inode, bool clean);
 void f2fs_balance_fs(struct f2fs_sb_info *sbi, bool need);
 void f2fs_balance_fs_bg(struct f2fs_sb_info *sbi, bool from_bg);
+int f2fs_submit_flush_wait(struct f2fs_sb_info *sbi,
+				struct block_device *bdev);
 int f2fs_issue_flush(struct f2fs_sb_info *sbi, nid_t ino);
 int f2fs_create_flush_cmd_control(struct f2fs_sb_info *sbi);
 int f2fs_flush_device_cache(struct f2fs_sb_info *sbi);
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index cc82d42ef14c..d68c903f1ad3 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -544,7 +544,7 @@ void f2fs_balance_fs_bg(struct f2fs_sb_info *sbi, bool from_bg)
 	f2fs_sync_fs(sbi->sb, 1);
 }
 
-static int __submit_flush_wait(struct f2fs_sb_info *sbi,
+int f2fs_submit_flush_wait(struct f2fs_sb_info *sbi,
 				struct block_device *bdev)
 {
 	int ret = blkdev_issue_flush(bdev);
@@ -562,12 +562,12 @@ static int submit_flush_wait(struct f2fs_sb_info *sbi, nid_t ino)
 	int i;
 
 	if (!f2fs_is_multi_device(sbi))
-		return __submit_flush_wait(sbi, sbi->sb->s_bdev);
+		return f2fs_submit_flush_wait(sbi, sbi->sb->s_bdev);
 
 	for (i = 0; i < sbi->s_ndevs; i++) {
 		if (!f2fs_is_dirty_device(sbi, ino, i, FLUSH_INO))
 			continue;
-		ret = __submit_flush_wait(sbi, FDEV(i).bdev);
+		ret = f2fs_submit_flush_wait(sbi, FDEV(i).bdev);
 		if (ret)
 			break;
 	}
@@ -748,7 +748,7 @@ int f2fs_flush_device_cache(struct f2fs_sb_info *sbi)
 			continue;
 
 		do {
-			ret = __submit_flush_wait(sbi, FDEV(i).bdev);
+			ret = f2fs_submit_flush_wait(sbi, FDEV(i).bdev);
 			if (ret)
 				f2fs_io_schedule_timeout(DEFAULT_IO_TIMEOUT);
 		} while (ret && --count);
diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
index f736052dea50..b69015f1dc67 100644
--- a/fs/f2fs/sysfs.c
+++ b/fs/f2fs/sysfs.c
@@ -852,6 +852,13 @@ static ssize_t __sbi_store(struct f2fs_attr *a,
 		return count;
 	}
 
+	if (!strcmp(a->attr.name, "flush_policy")) {
+		if (t >= BIT(FLUSH_POLICY_MAX))
+			return -EINVAL;
+		*ui = (unsigned int)t;
+		return count;
+	}
+
 	if (!strcmp(a->attr.name, "gc_boost_gc_multiple")) {
 		if (t < 1 || t > SEGS_PER_SEC(sbi))
 			return -EINVAL;
@@ -1175,6 +1182,7 @@ F2FS_SBI_GENERAL_RW_ATTR(blkzone_alloc_policy);
 #endif
 F2FS_SBI_GENERAL_RW_ATTR(carve_out);
 F2FS_SBI_GENERAL_RW_ATTR(reserved_pin_section);
+F2FS_SBI_GENERAL_RW_ATTR(flush_policy);
 
 /* STAT_INFO ATTR */
 #ifdef CONFIG_F2FS_STAT_FS
@@ -1371,6 +1379,7 @@ static struct attribute *f2fs_attrs[] = {
 	ATTR_LIST(max_read_extent_count),
 	ATTR_LIST(carve_out),
 	ATTR_LIST(reserved_pin_section),
+	ATTR_LIST(flush_policy),
 	NULL,
 };
 ATTRIBUTE_GROUPS(f2fs);
-- 
2.49.0



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