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From: Shakeel Butt To: Andrew Morton Cc: Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Qi Zheng , Meta kernel team , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel test robot Subject: Re: [PATCH] memcg: cache obj_stock by memcg, not by objcg pointer Message-ID: References: <20260515171953.2224503-1-shakeel.butt@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: A8D3280005 X-Rspam-User: X-Stat-Signature: 7izpsbq4rcb148z8rf1pgsxczax55wjb X-HE-Tag: 1779046484-486441 X-HE-Meta: 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 Im7fdCy8 Oi2HhoDTKyZNXUMiHYnOU6eEo1tM7yzEMJ2O4c0ji4nEEfZ8vD/QIKRaTRrnpvRyv2OxL1gk8BaUEIDQpA5WRDbjb6eFAy0XcwqABxUXooTblIfaO6tQWTUGbUnQ2kYM46V/q7rOiwO1lsIK0PA3nTTQHjnpvJoC7ONJoloKDAqvBr3exOtzM8O8+ZgBwgeVnIZeGYBGwFCaxrcCT01TzbH4mrk/ggwnCYLJel4AOfPdZzxqw8SJBBHsCSCgR9P7dImZy Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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.