The patch titled
Subject: Revert "mm:vmscan: fix inaccurate reclaim during proactive reclaim"
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
revert-mm-vmscan-fix-inaccurate-reclaim-during-proactive-reclaim.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/revert-mm-vmscan-fix-inaccurate-reclaim-during-proactive-reclaim.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: "T.J. Mercier" <tjmercier@xxxxxxxxxx>
Subject: Revert "mm:vmscan: fix inaccurate reclaim during proactive reclaim"
Date: Sun, 21 Jan 2024 21:44:12 +0000
This reverts commit 0388536ac29104a478c79b3869541524caec28eb.
Proactive reclaim on the root cgroup is 10x slower after this patch when
MGLRU is enabled, and completion times for proactive reclaim on much
smaller non-root cgroups take ~30% longer (with or without MGLRU). With
root reclaim before the patch, I observe average reclaim rates of ~70k
pages/sec before try_to_free_mem_cgroup_pages starts to fail and the
nr_retries counter starts to decrement, eventually ending the proactive
reclaim attempt. After the patch the reclaim rate is consistently ~6.6k
pages/sec due to the reduced nr_pages value causing scan aborts as soon as
SWAP_CLUSTER_MAX pages are reclaimed. The proactive reclaim doesn't
complete after several minutes because try_to_free_mem_cgroup_pages is
still capable of reclaiming pages in tiny SWAP_CLUSTER_MAX page chunks and
nr_retries is never decremented.
The docs for memory.reclaim say, "the kernel can over or under reclaim
from the target cgroup" which this patch was trying to fix. Revert it
until a less costly solution is found.
Link: https://lkml.kernel.org/r/20240121214413.833776-1-tjmercier@xxxxxxxxxx
Fixes: 0388536ac291 ("mm:vmscan: fix inaccurate reclaim during proactive reclaim")
Signed-off-by: T.J. Mercier <tjmercier@xxxxxxxxxx>
Cc: Efly Young <yangyifei03@xxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: T.J. Mercier <tjmercier@xxxxxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
--- a/mm/memcontrol.c~revert-mm-vmscan-fix-inaccurate-reclaim-during-proactive-reclaim
+++ a/mm/memcontrol.c
@@ -6977,8 +6977,8 @@ static ssize_t memory_reclaim(struct ker
lru_add_drain_all();
reclaimed = try_to_free_mem_cgroup_pages(memcg,
- min(nr_to_reclaim - nr_reclaimed, SWAP_CLUSTER_MAX),
- GFP_KERNEL, reclaim_options);
+ nr_to_reclaim - nr_reclaimed,
+ GFP_KERNEL, reclaim_options);
if (!reclaimed && !nr_retries--)
return -EAGAIN;
_
Patches currently in -mm which might be from tjmercier@xxxxxxxxxx are
revert-mm-vmscan-fix-inaccurate-reclaim-during-proactive-reclaim.patch
