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zram: clear IDLE flag after recompression

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commit f852190966 upstream.

Patch series "zram: IDLE flag handling fixes", v2.

zram can wrongly preserve ZRAM_IDLE flag on its entries which can result
in premature post-processing (writeback and recompression) of such
entries.

This patch (of 2)

Recompression should clear ZRAM_IDLE flag on the entries it has accessed,
because otherwise some entries, specifically those for which recompression
has failed, become immediate candidate entries for another post-processing
(e.g.  writeback).

Consider the following case:
- recompression marks entries IDLE every 4 hours and attempts
  to recompress them
- some entries are incompressible, so we keep them intact and
  hence preserve IDLE flag
- writeback marks entries IDLE every 8 hours and writebacks
  IDLE entries, however we have IDLE entries left from
  recompression, so writeback prematurely writebacks those
  entries.

The bug was reported by Shin Kawamura.

Link: https://lkml.kernel.org/r/20241028153629.1479791-1-senozhatsky@chromium.org
Link: https://lkml.kernel.org/r/20241028153629.1479791-2-senozhatsky@chromium.org
Fixes: 84b33bf788 ("zram: introduce recompress sysfs knob")
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reported-by: Shin Kawamura <kawasin@google.com>
Acked-by: Brian Geffon <bgeffon@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Sergey Senozhatsky
2024-10-29 00:36:14 +09:00
committed by Greg Kroah-Hartman
parent f8cca70b0e
commit 9a8b989d89
1 changed files with 7 additions and 0 deletions
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drivers/block/zram/zram_drv.c
+7
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@@ -1600,6 +1600,13 @@ static int zram_recompress(struct zram *zram, u32 index, struct page *page,
if (ret)
return ret;
/*
* We touched this entry so mark it as non-IDLE. This makes sure that
* we don't preserve IDLE flag and don't incorrectly pick this entry
* for different post-processing type (e.g. writeback).
*/
zram_clear_flag(zram, index, ZRAM_IDLE);
class_index_old = zs_lookup_class_index(zram->mem_pool, comp_len_old);
/*
* Iterate the secondary comp algorithms list (in order of priority)