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b=iKXpz5BQspSTB/yVdyil9C8T9ubHWY8dy7Fu6HvyNLXCWgAFgZHlou8L1dRh1Zs75 www38WX9HcC1KcjqWybnFDKl7yzmVBKK6cUPmp8Em6U8Ui/7b/3EPj8H1BV+l+kBGY vrhmK64tjy1wZk6jq1l7MtzWiGJvZLg6rtA3+mhY45dfu0YFjMfSHXp0Q6cum6PX5T yduq9ExJuohOhP8GXdZXpwItvJCZ44kgZcBnejO6MgeVYRY3gdF/g5wAxccms0lITo 5Ld9jDkL6I+Hbfusrq/seuR5n0AT+URmssp/mgtRG7vGAz9wtH/ZacSq0i1OJu3inY A/ZYRCXukx7bQ== Date: Thu, 12 Nov 2026 14:30:34 +0000 From: Harry Yoo To: Shakeel Butt Cc: Andrew Morton , Johannes Weiner , David Hildenbrand , Michal Hocko , Roman Gushchin , Muchun Song , Vlastimil Babka , Meta kernel team , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Chris Mason , stable@vger.kernel.org Subject: Re: [PATCH] memcg: flush nr_charged_bytes when the obj stock trylock fails Message-ID: References: <20261112013220.4064478-1-shakeel.butt@linux.dev> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261112013220.4064478-1-shakeel.butt@linux.dev> X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: DEB5C100010 X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Stat-Signature: syk36x6y6zxf35gzgh7545o7qs3axmfg X-Rspam-User: X-HE-Tag: 1794493836-348387 X-HE-Meta: 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 NEaUtdMQ GeikoauomL1qDl+qT6A8ulomeIVXSoH0mWRBHQV8pjILEwJXlyZg4FIDddZf8jgEIQj/4NH8STeC4V2zvy/SIWqPjBwcLw3E+EGrKTxQrexkA7FQLataAIMqfJGXU4YPjE+jfmbcr1hgQiLS2EpWv1TlH6RnreFmPpNkXae9H0/TandigF8A+IVM6+etQKX5y8pWuUBubPU5rt5imFdk9RiSJaabiQ3Qky7lHceZhTpP8gOMCBdD837e0eW8nrjSBRuczj31vqCmB82HtIR2KQxAntIs8UvyTP9PVko+XcE3OG4iJJufeyRPbjRg5pr9BfFFf Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Wed, Nov 11, 2026 at 05:32:20PM -0800, Shakeel Butt wrote: > When interrupt code, such as an RCU callback in softirq, runs on top of > a task that holds the obj stock lock, its trylock fails and the bytes go > to objcg->nr_charged_bytes. Nothing empties that counter while every CPU > using the objcg keeps it in its stock, so it can grow without limit. > > Users see memory.current and the "kernel" field of memory.stat keep > growing while the cgroup's real usage does not. With memory.high or > memory.max set, the cgroup is reclaimed, throttled or even OOM-killed > for memory it does not use. The counter is 32-bit, so after 4 GiB it > wraps, and those 4 GiB stay charged to the cgroup and its ancestors > until reboot, even after the cgroup is removed. > > Fix it by uncharging the whole pages in nr_charged_bytes whenever the > trylock fails. > > Fixes: 200577f69f29 ("memcg: objcg stock trylock without irq disabling") > Reported-by: Chris Mason > Signed-off-by: Shakeel Butt > Cc: stable@vger.kernel.org > --- Looks good to me, Reviewed-by: Harry Yoo (Meta) > mm/memcontrol.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index f5f567f7d4a9..091401cecf39 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -3553,6 +3553,8 @@ static void __refill_obj_stock(struct obj_cgroup *objcg, > int i, slot = -1, empty_slot = -1; > > if (!stock) { > + nr_bytes += atomic_read(&objcg->nr_charged_bytes) > + ? atomic_xchg(&objcg->nr_charged_bytes, 0) : 0; > nr_pages = nr_bytes >> PAGE_SHIFT; > nr_bytes = nr_bytes & (PAGE_SIZE - 1); > atomic_add(nr_bytes, &objcg->nr_charged_bytes); > -- > 2.53.0-Meta -- Cheers, Harry / Hyeonggon