linux-kernel - Re: [PATCH v2 00/28] Eliminate Dying Memory Cgroup

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Message-ID: <aUunxoFxrx5hiIPy@hyeyoo>
Date: Wed, 24 Dec 2025 17:43:50 +0900
From: Harry Yoo <harry.yoo@...cle.com>
To: Yosry Ahmed <yosry.ahmed@...ux.dev>
Cc: Qi Zheng <qi.zheng@...ux.dev>, hannes@...xchg.org, hughd@...gle.com,
        mhocko@...e.com, roman.gushchin@...ux.dev, shakeel.butt@...ux.dev,
        muchun.song@...ux.dev, david@...nel.org, lorenzo.stoakes@...cle.com,
        ziy@...dia.com, imran.f.khan@...cle.com, kamalesh.babulal@...cle.com,
        axelrasmussen@...gle.com, yuanchu@...gle.com, weixugc@...gle.com,
        chenridong@...weicloud.com, mkoutny@...e.com,
        akpm@...ux-foundation.org, hamzamahfooz@...ux.microsoft.com,
        apais@...ux.microsoft.com, lance.yang@...ux.dev, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        Qi Zheng <zhengqi.arch@...edance.com>
Subject: Re: [PATCH v2 00/28] Eliminate Dying Memory Cgroup

On Tue, Dec 23, 2025 at 08:04:50PM +0000, Yosry Ahmed wrote:
> I think there might be a problem with non-hierarchical stats on cgroup
> v1, I brought it up previously [*]. I am not sure if this was addressed
> but I couldn't immediately find anything.

Hi, Yosry. Thanks for bringing this up!

> In short, if memory is charged to a dying cgroup at the time of
> reparenting, when the memory gets uncharged the stats updates will occur
> at the parent. This will update both hierarchical and non-hierarchical
> stats of the parent, which would corrupt the parent's non-hierarchical
> stats (because those counters were never incremented when the memory was
> charged).

Hmm, I wonder if this only applies to LRU pages.

In theory we should have this problem for NR_SLAB{UN,}RECLAIMABLE_B
because we already reparent objcgs, or am I missing something?

> [*]https://lore.kernel.org/all/CAJD7tkazvC*kZgGaV3idapQp-zPFaWBxoHwnrqTFoodHZGQcPA@mail.gmail.com/