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AJvYcCX8k1av5OFV/ojTfMsDh42Z6uBw3U5EEIANEcRcC2Nzyah8AnSrXnZsMZaqqU+4swWOx/EmubVn8w==@kvack.org X-Gm-Message-State: AOJu0YykW3mg3o+fTnjbsvkEFDZJnSx9FClGIq+Te9eqht08VD2sJiWQ CiJzz/t23yGhSZPOcuNX/mqFRcene1/818og9S/PSHy0uJAmyY17kmE/F1ieCSeMHeyzp3RbwN0 ekfI+84mQK86V0ObrUZSpB/wAiAXh5V/pjDyB X-Google-Smtp-Source: AGHT+IEf8Xan5YN2lxVFxkPlg5MJ8Vug9skFQs3j11e9BUUzumrE5tyW5bdmM5Xp8uNUl5TYbvlM0f6UV9BYTCns0FE= X-Received: by 2002:a05:6214:4588:b0:6d1:8261:174f with SMTP id 6a1803df08f44-6d185816d6fmr136359396d6.36.1730135343409; Mon, 28 Oct 2024 10:09:03 -0700 (PDT) MIME-Version: 1.0 References: <20241027011959.9226-1-21cnbao@gmail.com> <678a1e30-4962-48de-b5cb-03a1b4b9db1b@gmail.com> <6303e3c9-85d5-40f5-b265-70ecdb02d5ba@gmail.com> In-Reply-To: <6303e3c9-85d5-40f5-b265-70ecdb02d5ba@gmail.com> From: Yosry Ahmed Date: Mon, 28 Oct 2024 10:08:26 -0700 Message-ID: Subject: Re: [PATCH RFC] mm: count zeromap read and set for swapout and swapin To: Usama Arif Cc: Nhat Pham , Barry Song <21cnbao@gmail.com>, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Barry Song , Chengming Zhou , Johannes Weiner , David Hildenbrand , Hugh Dickins , Matthew Wilcox , Shakeel Butt , Andi Kleen , Baolin Wang , Chris Li , "Huang, Ying" , Kairui Song , Ryan Roberts , joshua.hahnjy@gmail.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 3534BC002D X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: i35c6byfa3gdazipra8b6gutt3mr7m6b X-HE-Tag: 1730135333-980434 X-HE-Meta: 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 hQvn4nx0 2gY5YuIsTHhUQ7VrJ0L4mQ/lr6El+ZyYdgdfUPQQXcWhRn+FkV6UQMiDxEUQWVkJXT135xhBfz/sUYlW9Gc9e69IUfammws/IVNX9F9Yu6MoZxv3D1ylLrYjE/kLXej5K04RRcop/Y07716hJqL1tUYJTrt3BRxDUv5YirJahDiiSrdJMmpvs6L8UbFfXX3jPLPumqkWzr28CzEIyzv3Ucnk+FBfQDn+cmSmm0FacCUX2ZVJxaBFndQBttTgZ2JLfBjL9BM/dtSbxW8cbex+py1vcMHtIImBlyxb/ X-Bogosity: Ham, tests=bogofilter, spamicity=0.000003, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Oct 28, 2024 at 10:00=E2=80=AFAM Usama Arif wrote: > > > > On 28/10/2024 16:33, Nhat Pham wrote: > > On Mon, Oct 28, 2024 at 5:23=E2=80=AFAM Usama Arif wrote: > >> > >> I wonder if instead of having counters, it might be better to keep tra= ck > >> of the number of zeropages currently stored in zeromap, similar to how > >> zswap_same_filled_pages did it. It will be more complicated then this > >> patch, but would give more insight of the current state of the system. > >> > >> Joshua (in CC) was going to have a look at that. > > > > I don't think one can substitute for the other. > > Yes agreed, they have separate uses and provide different information, bu= t > maybe wasteful to have both types of counters? They are counters so maybe > dont consume too much resources but I think we should still think about > it.. Not for or against here, but I would say that statement is debatable at best for memcg stats :) Each new counter consumes 2 longs per-memcg per-CPU (see memcg_vmstats_percpu), about 16 bytes, which is not a lot but it can quickly add up with a large number of CPUs/memcgs/stats. Also, when flushing the stats we iterate all of them to propagate updates from per-CPU counters. This is already a slowpath so adding one stat is not a big deal, but again because we iterate all stats on multiple CPUs (and sometimes on each node as well), the overall flush latency becomes a concern sometimes. All of that is not to say we shouldn't add more memcg stats, but we have to be mindful of the resources.