linux-kernel - Re: [PATCH v6] mm/vmscan: fix demotion targets checks in reclaim/demotion

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Message-ID: <aV0a5pYLNV61WJGk@gourry-fedora-PF4VCD3F>
Date: Tue, 6 Jan 2026 09:23:34 -0500
From: Gregory Price <gourry@...rry.net>
To: Bing Jiao <bingjiao@...gle.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, longman@...hat.com, hannes@...xchg.org,
	mhocko@...nel.org, roman.gushchin@...ux.dev, shakeel.butt@...ux.dev,
	muchun.song@...ux.dev, tj@...nel.org, mkoutny@...e.com,
	david@...nel.org, zhengqi.arch@...edance.com,
	lorenzo.stoakes@...cle.com, axelrasmussen@...gle.com,
	chenridong@...weicloud.com, yuanchu@...gle.com, weixugc@...gle.com,
	cgroups@...r.kernel.org
Subject: Re: [PATCH v6] mm/vmscan: fix demotion targets checks in
 reclaim/demotion

On Tue, Jan 06, 2026 at 07:56:54AM +0000, Bing Jiao wrote:
> 
> Bug 1 reproduction:
>   Assume a system with 4 nodes, where nodes 0-1 are top-tier and
>   nodes 2-3 are far-tier memory. All nodes have equal capacity.
> 
>   Test script:
>     echo 1 > /sys/kernel/mm/numa/demotion_enabled
>     mkdir /sys/fs/cgroup/test
>     echo +cpuset > /sys/fs/cgroup/cgroup.subtree_control
>     echo "0-2" > /sys/fs/cgroup/test/cpuset.mems
>     echo $$ > /sys/fs/cgroup/test/cgroup.procs
>     swapoff -a
>     # Expectation: Should respect node 0-2 limit.
>     # Observation: Node 3 shows significant allocation (MemFree drops)
>     stress-ng --oomable --vm 1 --vm-bytes 150% --mbind 0,1
> 
> Bug 2 reproduction:
>   Assume a system with 6 nodes, where nodes 0-2 are top-tier,
>   node 3 is a far-tier node, and nodes 4-5 are the farthest-tier nodes.
>   All nodes have equal capacity.
> 
>   Test script:
>     echo 1 > /sys/kernel/mm/numa/demotion_enabled
>     mkdir /sys/fs/cgroup/test
>     echo +cpuset > /sys/fs/cgroup/cgroup.subtree_control
>     echo "0-2,4-5" > /sys/fs/cgroup/test/cpuset.mems
>     echo $$ > /sys/fs/cgroup/test/cgroup.procs
>     swapoff -a
>     # Expectation: Pages are demoted to Nodes 4-5
>     # Observation: No pages are demoted before oom.
>     stress-ng --oomable --vm 1 --vm-bytes 150% --mbind 0,1,2
> 
> Fixes: 7d709f49babc ("vmscan,cgroup: apply mems_effective to reclaim")
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Bing Jiao <bingjiao@...gle.com>

This looks ok now, haven't tested it myself yet, but looks good.

Thank you for the fix.

Reviewed-by: Gregory Price <gourry@...rry.net>

~Gregory