linux-kernel - [PATCH 4.9 133/153] f2fs: avoid to issue redundant discard commands

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Date:   Fri, 10 Mar 2017 10:09:26 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Damien Le Moal <damien.lemoal@....com>,
        Jaegeuk Kim <jaegeuk@...nel.org>
Subject: [PATCH 4.9 133/153] f2fs: avoid to issue redundant discard commands

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jaegeuk Kim <jaegeuk@...nel.org>

commit 8b107f5b97772c7c0c218302e9a4d15b4edf50b4 upstream.

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: Damien Le Moal <damien.lemoal@....com>
Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/f2fs/segment.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -813,6 +813,8 @@ next:
 		start = start_segno + sbi->segs_per_sec;
 		if (start < end)
 			goto next;
+		else
+			end = start - 1;
 	}
 	mutex_unlock(&dirty_i->seglist_lock);