The patch titled
Subject: zswap: memcontrol: implement zswap writeback disabling (fix)
has been added to the -mm mm-unstable branch. Its filename is
zswap-memcontrol-implement-zswap-writeback-disabling-fix.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/zswap-memcontrol-implement-zswap-writeback-disabling-fix.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: Nhat Pham <nphamcs@xxxxxxxxx>
Subject: zswap: memcontrol: implement zswap writeback disabling (fix)
Date: Wed, 20 Dec 2023 16:57:25 -0800
Add a caveat about recurring zswap store failures leading to reclaim
inefficiency.
Link: https://lkml.kernel.org/r/20231221005725.3446672-1-nphamcs@xxxxxxxxx
Suggested-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
Signed-off-by: Nhat Pham <nphamcs@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/admin-guide/cgroup-v2.rst | 5 ++++-
Documentation/admin-guide/mm/zswap.rst | 4 ++++
2 files changed, 8 insertions(+), 1 deletion(-)
--- a/Documentation/admin-guide/cgroup-v2.rst~zswap-memcontrol-implement-zswap-writeback-disabling-fix
+++ a/Documentation/admin-guide/cgroup-v2.rst
@@ -1686,7 +1686,10 @@ PAGE_SIZE multiple when read back.
When this is set to 0, all swapping attempts to swapping devices
are disabled. This included both zswap writebacks, and swapping due
- to zswap store failure.
+ to zswap store failures. If the zswap store failures are recurring
+ (for e.g if the pages are incompressible), users can observe
+ reclaim inefficiency after disabling writeback (because the same
+ pages might be rejected again and again).
Note that this is subtly different from setting memory.swap.max to
0, as it still allows for pages to be written to the zswap pool.
--- a/Documentation/admin-guide/mm/zswap.rst~zswap-memcontrol-implement-zswap-writeback-disabling-fix
+++ a/Documentation/admin-guide/mm/zswap.rst
@@ -159,6 +159,10 @@ zswap itself) on a cgroup-basis as follo
echo 0 > /sys/fs/cgroup/<cgroup-name>/memory.zswap.writeback
+Note that if the store failures are recurring (for e.g if the pages are
+incompressible), users can observe reclaim inefficiency after disabling
+writeback (because the same pages might be rejected again and again).
+
When there is a sizable amount of cold memory residing in the zswap pool, it
can be advantageous to proactively write these cold pages to swap and reclaim
the memory for other use cases. By default, the zswap shrinker is disabled.
_
Patches currently in -mm which might be from nphamcs@xxxxxxxxx are
zswap-memcontrol-implement-zswap-writeback-disabling.patch
zswap-memcontrol-implement-zswap-writeback-disabling-fix.patch
