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

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Message-ID: <aU5wYLrE2S1B9y_M@hyeyoo>
Date: Fri, 26 Dec 2025 20:24:16 +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 Wed, Dec 24, 2025 at 02:51:12PM +0000, Yosry Ahmed wrote:
> December 24, 2025 at 12:43 AM, "Harry Yoo" <harry.yoo@...cle.com> wrote:
> 
> 
> > 
> > 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?
> 
> We do, but we don't expose these stats in cgroup v1, and we don't expose non-hierarchical stats in cgroup v2.

Oops, right.
I was missing that. Thanks!

-- 
Cheers,
Harry / Hyeonggon