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Mon, 08 Jun 2026 20:18:39 -0700 (PDT) Message-ID: <1c25650e-bf98-2863-d505-9b94c385668b@gmail.com> Date: Tue, 9 Jun 2026 11:18:26 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.15.0 Subject: Re: [PATCH v3 1/4] mm/zswap: Make shrink_worker writeback cursor per-memcg To: Nhat Pham , Yosry Ahmed , shakeel.butt@linux.dev Cc: akpm@linux-foundation.org, tj@kernel.org, hannes@cmpxchg.org, mhocko@kernel.org, mkoutny@suse.com, chengming.zhou@linux.dev, muchun.song@linux.dev, roman.gushchin@linux.dev, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, Hao Jia References: <20260526114601.67041-1-jiahao.kernel@gmail.com> <20260526114601.67041-2-jiahao.kernel@gmail.com> <8c0e60e1-5713-69f0-a687-088c87e75764@gmail.com> <9898f83d-fae9-e284-6b85-c7f4089840a0@gmail.com> <90730fa7-62e7-d5f4-b638-23b22a8509f2@gmail.com> From: Hao Jia In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2026/6/9 02:01, Nhat Pham wrote: > On Mon, Jun 8, 2026 at 9:48 AM Yosry Ahmed wrote: >> >>> But OTOH, this does seem like a recipe for inefficient reclaim. We >>> might exhaust hotter memory of a cgroup while sparing colder memory of >>> another cgroup... But maybe if they're all cold anyway, then who >>> cares, and eventually you'll get to the cold stuff of other child? >> >> Forgot to respond to this part, the unfairness is limited to the batch >> size per-invocation, so it should be fine as long as you don't divide >> the amount over 100 iterations for some reason. Also yes, all memory >> in zswap is cold, the relative coldness is not that important (e.g. >> compared to relative coldness during reclaim). > > Ok then yeah, I think we should shelve per-memcg cursor for the next > version. Down the line, if we have more data that unfairness is an > issue, we can always fix it. One step at a time :) Thanks a lot to Yosry, Nhat, and Shakeel for the great suggestions! Let me summarize what I plan to do in the next version to make sure we are on the same page: - Drop the per-memcg cursor and keep the root cgroup cursor (zswap_next_shrink) logic intact. - Stick to using the zswap_writeback_only key, and change the proactive writeback size to use the compressed size. - Consolidate and reuse the logic between shrink_worker() and shrink_memcg(). Enable batch writeback in the shrink_worker() path, while keeping the writeback behavior in the zswap_store() path unchanged. Please let me know if I missed or misunderstood anything. Thanks again for clearing things up! Thanks， Hao