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From: Shakeel Butt <shakeel.butt@linux.dev>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>,
	Michal Hocko <mhocko@kernel.org>,
	 Roman Gushchin <roman.gushchin@linux.dev>,
	Muchun Song <muchun.song@linux.dev>,
	 Qi Zheng <qi.zheng@linux.dev>,
	Meta kernel team <kernel-team@meta.com>,
	linux-mm@kvack.org,  cgroups@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	 kernel test robot <oliver.sang@intel.com>
Subject: Re: [PATCH] memcg: cache obj_stock by memcg, not by objcg pointer
Date: Sun, 17 May 2026 12:34:34 -0700	[thread overview]
Message-ID: <agd-gbYnVyaaiLH7@linux.dev> (raw)
In-Reply-To: <agdnTPXhuepuu7hG@linux.dev>

On Fri, May 15, 2026 at 11:42:39AM -0700, Shakeel Butt wrote:
[...]
> > Will sharing the reserve between per-node sibling objcgs without updating
> > stock->cached_objcg break the page multiple invariant in
> > obj_cgroup_release()?
> > 
> > If an allocation for objcg_B consumes bytes originally funded by objcg_A,
> > and the stock is later drained, those borrowed bytes are flushed into
> > objcg_A->nr_charged_bytes.
> > 
> > When obj_cgroup_release() is invoked, nr_charged_bytes will not be an
> > exact multiple of PAGE_SIZE. Will this trigger
> > WARN_ON_ONCE(nr_bytes & (PAGE_SIZE - 1)) and truncate the remainder,
> > permanently leaking the page charge from the memcg?
> 
> This is actually a very good point and need more thought.
> 

I think we can handle this simply by taking over objcg->nr_charged_bytes into
the stock.



  reply	other threads:[~2026-05-17 19:34 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-05-15 17:19 [PATCH] memcg: cache obj_stock by memcg, not by objcg pointer Shakeel Butt
2026-05-15 18:42 ` Shakeel Butt
2026-05-17 19:34   ` Shakeel Butt [this message]
2026-05-16  6:58 ` [syzbot ci] " syzbot ci

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