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Thu, 08 Apr 2021 09:24:56 -0700 (PDT) MIME-Version: 1.0 References: <20210408143155.2679744-1-hannes@cmpxchg.org> In-Reply-To: <20210408143155.2679744-1-hannes@cmpxchg.org> From: Shakeel Butt Date: Thu, 8 Apr 2021 09:24:45 -0700 Message-ID: Subject: Re: [PATCH] mm: page_counter: mitigate consequences of a page_counter underflow To: Johannes Weiner Cc: Andrew Morton , Michal Hocko , Hugh Dickins , Roman Gushchin , Linux MM , Cgroups , LKML , Kernel Team Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: A0D8CE000108 X-Stat-Signature: pptpjiste1tnam43zjgxr3ebqyt5bdgr Received-SPF: none (google.com>: No applicable sender policy available) receiver=imf30; identity=mailfrom; envelope-from=""; helo=mail-lf1-f43.google.com; client-ip=209.85.167.43 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1617899091-629155 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Apr 8, 2021 at 7:31 AM Johannes Weiner wrote: > > When the unsigned page_counter underflows, even just by a few pages, a > cgroup will not be able to run anything afterwards and trigger the OOM > killer in a loop. > > Underflows shouldn't happen, but when they do in practice, we may just > be off by a small amount that doesn't interfere with the normal > operation - consequences don't need to be that dire. > > Reset the page_counter to 0 upon underflow. We'll issue a warning that > the accounting will be off and then try to keep limping along. > > [ We used to do this with the original res_counter, where it was a > more straight-forward correction inside the spinlock section. I > didn't carry it forward into the lockless page counters for > simplicity, but it turns out this is quite useful in practice. ] > > Signed-off-by: Johannes Weiner Reviewed-by: Shakeel Butt