+ zram-clear-idle-flag-after-recompression.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

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@chromium.org>
Subject: zram: clear IDLE flag after recompression
Date: Mon, 28 Oct 2024 16:34:57 +0900

Patch series "zram: IDLE flag handling fixes".

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 entires 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.

Link: https://lkml.kernel.org/r/20241028073529.1383980-1-senozhatsky@chromium.org
Link: https://lkml.kernel.org/r/20241028073529.1383980-2-senozhatsky@chromium.org
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reported-by: Shin Kawamura <kawasin@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 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@chromium.org 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