The patch titled
Subject: zram: clear IDLE flag after recompression
has been added to the -mm mm-unstable branch. Its filename is
zram-clear-idle-flag-after-recompression.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/zram-clear-idle-flag-after-recompression.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
Subject: zram: clear IDLE flag after recompression
Date: Tue, 29 Oct 2024 00:36:14 +0900
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@xxxxxxxxxxxx
Link: https://lkml.kernel.org/r/20241028153629.1479791-2-senozhatsky@xxxxxxxxxxxx
Fixes: 84b33bf78889 ("zram: introduce recompress sysfs knob")
Signed-off-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
Reported-by: Shin Kawamura <kawasin@xxxxxxxxxx>
Acked-by: Brian Geffon <bgeffon@xxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/block/zram/zram_drv.c | 7 +++++++
1 file changed, 7 insertions(+)
--- a/drivers/block/zram/zram_drv.c~zram-clear-idle-flag-after-recompression
+++ a/drivers/block/zram/zram_drv.c
@@ -1864,6 +1864,13 @@ static int recompress_slot(struct zram *
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)
_
Patches currently in -mm which might be from senozhatsky@xxxxxxxxxxxx are
zram-introduce-zram_pp_slot-flag.patch
zram-permit-only-one-post-processing-operation-at-a-time.patch
zram-rework-recompress-target-selection-strategy.patch
zram-rework-recompress-target-selection-strategy-fix.patch
zram-rework-writeback-target-selection-strategy.patch
zram-do-not-mark-idle-slots-that-cannot-be-idle.patch
zram-reshuffle-zram_free_page-flags-operations.patch
zram-remove-under_wb-and-simplify-writeback.patch
zram-do-not-open-code-comp-priority-0.patch
zram-clear-idle-flag-after-recompression.patch
zram-clear-idle-flag-in-mark_idle.patch
