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Mon, 28 Aug 2023 10:29:20 -0700 (PDT) MIME-Version: 1.0 References: <20230821205458.1764662-4-yosryahmed@google.com> <599b167c-deaf-4b92-aa8b-5767b8608483@redhat.com> In-Reply-To: <599b167c-deaf-4b92-aa8b-5767b8608483@redhat.com> From: Yosry Ahmed Date: Mon, 28 Aug 2023 10:28:44 -0700 Message-ID: Subject: Re: [PATCH 3/3] mm: memcg: use non-unified stats flushing for userspace reads To: Waiman Long Cc: Shakeel Butt , Michal Hocko , Andrew Morton , Johannes Weiner , Roman Gushchin , Muchun Song , Ivan Babrou , Tejun Heo , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 56DF71C0031 X-Rspam-User: X-Stat-Signature: h6uspnpcjnpr8mogexb1ot1gmqpqnycq X-Rspamd-Server: rspam03 X-HE-Tag: 1693243762-891882 X-HE-Meta: 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 5qItFo2Q HnQnpJABscDZh9uVcFtGbKhSl/IZgaET6dC+aRYhCvgDQxy6FxU/e492e2YSwbXmyBeaAE2SSg7fbgwwytNa9l58a1w7KgwfxgV+xOqu5glInCOu3CJTDVqmR6S0dyHDh6EHDNXj+tqcvZmfxQ7ciIlvBoFalbXTobll0ek1xBwV4fVNMhJNV2/Wd9zuQa+JKqiXeqhSLk4t4dk8IXtVkJsb3Szm0KSxXH3rZsHhFwf9eA+bwMwrthSP4OA== 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 Mon, Aug 28, 2023 at 10:27=E2=80=AFAM Waiman Long w= rote: > > > On 8/28/23 13:07, Yosry Ahmed wrote: > > > >> Here I agree with you. Let's go with the approach which is easy to > >> undo for now. Though I prefer the new explicit interface for flushing, > >> that step would be very hard to undo. Let's reevaluate if the proposed > >> approach shows negative impact on production traffic and I think > >> Cloudflare folks can give us the results soon. > > Do you prefer we also switch to using a mutex (with preemption > > disabled) to avoid the scenario Michal described where flushers give > > up the lock and sleep resulting in an unbounded wait time in the worst > > case? > > Locking with mutex with preemption disabled is an oxymoron. Use spinlock > if you want to have preemption disabled. The purpose of usiing mutex is > to allow the lock owner to sleep, but you can't sleep with preemption > disabled. You need to enable preemption first. You can disable > preemption for a short time in a non-sleeping section of the lock > critical section, but I would not recommend disabling preemption for the > whole critical section. I thought using a mutex with preemption disabled would at least allow waiters to sleep rather than spin, is this not correct (or doesn't matter) ? > > Cheers, > Longman >