f2fs: introduce sysfs entry to control in-place-update policy
This patch introduces new sysfs entries for users to control the policy of
in-place-updates, namely IPU, in f2fs.
Sometimes f2fs suffers from performance degradation due to its out-of-place
update policy that produces many additional node block writes.
If the storage performance is very dependant on the amount of data writes
instead of IO patterns, we'd better drop this out-of-place update policy.
This patch suggests 5 polcies and their triggering conditions as follows.
[sysfs entry name = ipu_policy]
0: F2FS_IPU_FORCE all the time,
1: F2FS_IPU_SSR if SSR mode is activated,
2: F2FS_IPU_UTIL if FS utilization is over threashold,
3: F2FS_IPU_SSR_UTIL if SSR mode is activated and FS utilization is over
threashold,
4: F2FS_IPU_DISABLE disable IPU. (=default option)
[sysfs entry name = 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.
For more details, see need_inplace_update() in segment.h.
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>
diff --git a/Documentation/filesystems/f2fs.txt b/Documentation/filesystems/f2fs.txt
index a3fe811..1a94ac7 100644
--- a/Documentation/filesystems/f2fs.txt
+++ b/Documentation/filesystems/f2fs.txt
@@ -171,6 +171,17 @@
conduct checkpoint to reclaim the prefree segments
to free segments. By default, 100 segments, 200MB.
+ ipu_policy This parameter controls the policy of in-place
+ 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.
+
+ 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.
+
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USAGE
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