linux-kernel - [PATCH 2/2] Revert "f2fs: do not issue small discard commands during checkpoint"

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Message-Id: <20230730142552.3918623-2-chao@kernel.org>
Date:   Sun, 30 Jul 2023 22:25:52 +0800
From:   Chao Yu <chao@...nel.org>
To:     jaegeuk@...nel.org
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, Chao Yu <chao@...nel.org>
Subject: [PATCH 2/2] Revert "f2fs: do not issue small discard commands during checkpoint"

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 9ac00e7cef10 ("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 9ac00e7cef10 ("f2fs: do not issue small discard
commands during checkpoint") in order to fix this issue.

Fixes: 9ac00e7cef10 ("f2fs: do not issue small discard commands during checkpoint")
Signed-off-by: Chao Yu <chao@...nel.org>
---
 fs/f2fs/segment.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 6e5d1039ca76..1f0a25011687 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -2195,7 +2195,7 @@ void f2fs_clear_prefree_segments(struct f2fs_sb_info *sbi,
 			len = next_pos - cur_pos;

 			if (f2fs_sb_has_blkzoned(sbi) ||
-					!force || len < cpc->trim_minlen)
+			    (force && len < cpc->trim_minlen))
 				goto skip;

 			f2fs_issue_discard(sbi, entry->start_blkaddr + cur_pos,
-- 
2.40.1