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Previously, we have two mechanisms to cache & submit small discards:
a) set max small discard number in /sys/fs/f2fs/vdb/max_small_discards,
and checkpoint will cache small discard candidates w/ configured maximum
number.
b) call FITRIM ioctl, also, checkpoint in f2fs_trim_fs() will cache small
discard candidates w/ configured discard granularity, but w/o limitation
of number. FSTRIM interface is asynchronized, so it won't submit discard
directly.
Finally, discard thread will submit them in background periodically.
However, after commit 9ac00e7cef ("f2fs: do not issue small discard
commands during checkpoint"), the mechanism a) is broken, since no matter
how we configure the sysfs entry /sys/fs/f2fs/vdb/max_small_discards,
checkpoint will not cache small discard candidates any more.
echo 0 > /sys/fs/f2fs/vdb/max_small_discards
xfs_io -f /mnt/f2fs/file -c "pwrite 0 2m" -c "fsync"
xfs_io /mnt/f2fs/file -c "fpunch 0 4k"
sync
cat /proc/fs/f2fs/vdb/discard_plist_info |head -2
echo 100 > /sys/fs/f2fs/vdb/max_small_discards
rm /mnt/f2fs/file
xfs_io -f /mnt/f2fs/file -c "pwrite 0 2m" -c "fsync"
xfs_io /mnt/f2fs/file -c "fpunch 0 4k"
sync
cat /proc/fs/f2fs/vdb/discard_plist_info |head -2
Before the patch:
Discard pend list(Show diacrd_cmd count on each entry, .:not exist):
0 . . . . . . . .
Discard pend list(Show diacrd_cmd count on each entry, .:not exist):
0 3 1 . . . . . .
After the patch:
Discard pend list(Show diacrd_cmd count on each entry, .:not exist):
0 . . . . . . . .
Discard pend list(Show diacrd_cmd count on each entry, .:not exist):
0 . . . . . . . .
This patch reverts commit 9ac00e7cef ("f2fs: do not issue small discard
commands during checkpoint") in order to fix this issue.
Fixes: 9ac00e7cef ("f2fs: do not issue small discard commands during checkpoint")
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>