f2fs: give an option to enable in-place-updates during fsync to users

If user wrote F2FS_IPU_FSYNC:4 in /sys/fs/f2fs/ipu_policy, f2fs_sync_file
only starts to try in-place-updates.
And, if the number of dirty pages is over /sys/fs/f2fs/min_fsync_blocks, it
keeps out-of-order manner. Otherwise, it triggers in-place-updates.

This may be used by storage showing very high random write performance.

For example, it can be used when,

Seq. writes (Data) + wait + Seq. writes (Node)

is pretty much slower than,

Rand. writes (Data)

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

1 files changed, 8 insertions, 1 deletions

diff --git a/Documentation/filesystems/f2fs.txt b/Documentation/filesystems/f2fs.txt
index a2046a7d0a9d..d010da85a769 100644
--- a/Documentation/filesystems/f2fs.txt
+++ b/Documentation/filesystems/f2fs.txt
@@ -194,13 +194,20 @@ Files in /sys/fs/f2fs/<devname>
                               updates in f2fs. There are five policies:
                                0: F2FS_IPU_FORCE, 1: F2FS_IPU_SSR,
                                2: F2FS_IPU_UTIL,  3: F2FS_IPU_SSR_UTIL,
-                               4: F2FS_IPU_DISABLE.
+                               4: F2FS_IPU_FSYNC, 5: F2FS_IPU_DISABLE.
 
  min_ipu_util                 This parameter controls the threshold to trigger
                               in-place-updates. The number indicates percentage
                               of the filesystem utilization, and used by
                               F2FS_IPU_UTIL and F2FS_IPU_SSR_UTIL policies.
 
+ min_fsync_blocks             This parameter controls the threshold to trigger
+                              in-place-updates when F2FS_IPU_FSYNC mode is set.
+                              The number indicates the number of dirty pages
+                              when fsync needs to flush on its call path. If
+                              the number is less than this value, it triggers
+                              in-place-updates.
+
  max_victim_search            This parameter controls the number of trials to
                               find a victim segment when conducting SSR and
                               cleaning operations. The default value is 4096