linux-kernel - [PATCH] f2fs: avoid to issue redundant discard commands

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Message-Id: <20170227214355.8405-1-jaegeuk@kernel.org>
Date:   Mon, 27 Feb 2017 13:43:55 -0800
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Cc:     Jaegeuk Kim <jaegeuk@...nel.org>, stable@...r.kernel.org,
        Damien Le Moal <damien.lemoal@....com>
Subject: [PATCH] f2fs: avoid to issue redundant discard commands

If segs_per_sec is over 1 like under SMR, previously f2fs issues discard
commands redundantly on the same section, since we didn't move end position
for the previous discard command.

E.g.,

                       start  end
                         |    |
      prefree_bitmap = [01111100111100]

And, after issue discard for this section,
                             end      start
                              |        |
      prefree_bitmap = [01111100111100]

Select this section again by searching from (end + 1),
                             start  end
                                |   |
      prefree_bitmap = [01111100111100]

Fixes: 36abef4e796d38 ("f2fs: introduce mode=lfs mount option")
Cc: <stable@...r.kernel.org>
Cc: Damien Le Moal <damien.lemoal@....com>
Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
---
 fs/f2fs/segment.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 9006d8ed6f52..4bd7a8b19332 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -1036,6 +1036,8 @@ void clear_prefree_segments(struct f2fs_sb_info *sbi, struct cp_control *cpc)
 		start = start_segno + sbi->segs_per_sec;
 		if (start < end)
 			goto next;
+		else
+			end = start - 1;
 	}
 	mutex_unlock(&dirty_i->seglist_lock);
 
-- 
2.11.0