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Wed, 28 Oct 2026 18:48:55 -0700 (PDT) Received: from google.com ([2a00:79e0:2031:6:f72e:e03e:c64e:b5b3]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-1a75d85f23dsm8564749c88.11.2026.10.28.18.48.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 28 Oct 2026 18:48:54 -0700 (PDT) Date: Thu, 29 Oct 2026 10:48:50 +0900 From: Sergey Senozhatsky To: Nhat Pham Cc: Xueyuan Chen , Barry Song , Yosry Ahmed , Johannes Weiner , Brian Geffon , Minchan Kim , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, xueyuan.chen21@gmail.com, Sergey Senozhatsky Subject: Re: [RFC PATCH 0/2] mm: zsmalloc: make shrinker compaction budget-aware Message-ID: References: <47ed45b5-de67-41aa-aa21-a3ba3479a7cc@vivo.com> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 80AE340005 X-Stat-Signature: pir3a5s1nr5fmzejiybp55bugygjihsp X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=no autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1793238536-100670 X-HE-Meta: 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 yt5/sRwm MNrCQDfqGBm63YLJQHX97c5dCSJ9SINKAhsruRmhh9UdmNCdij4YqFYyjraqfrEaJ7xb4QP+MXDyZhvWYssMzRDVs4cChoPMQ50e1YrSW5kcHrStb6pm37EqMo3kutLqFCMBwkHgXdwUf/1P75r31PvjrfInaxTvlfJE6Dks40tFQj2OkkTWz7oyH7bvtMAmqC1wvE2HKV/oA4Y5LAuQhbO3kvA6RYUM7ghIVy4+5FGcqHz2r6zhy413ecE++PcPKimkJFSwczSneXXOnQXgIC9O1ugXJp00VBDevpEkyEHEzGXAmoJBA+ysgIzyOLYjDklt2Q0t1RiVUccPNYucK9a4/pbjO47WVhPh9gmnezBhlHM/q+1ZTn7VOjX5FfnUWoD4XvAAQ5E7zCDHHhH6Oh/Am8gDQ5uz5fQmG/pTupof2xtrFwOA9FmoywQ== 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 (26/10/29 10:43), Sergey Senozhatsky wrote: [..] > > Hmm we'd need to collect more data in our workloads to determine, but > > if we can compute compactable ratio (freeable_pages / total_pages) on > > a per size class basis, can we just skip the size class whose ratio is > > too bad? Would that at least cut down on the vast majority of > > fruitless memcpys and lock acquisitions etc? > > > > I'm always a bit hesitant to over-rely on userspace, especially when > > kernel has information to do something smart about it. It might not > > react in time, and many proactive reclaiming schemes back off under > > heavy memory pressure. > > Apologies for the delay. > > The thing about shrinker compaction is that it's sort of on the > wrong end. It doesn't trigger compaction when memory is plentiful, > no matter the internal fragmentation rate, and start firing compaction > scans when memory pressure hits. The problem with this is that, now > compaction moves objects (if can compact zspages) and releases empty > zspages, in parallel with potentially heavy swapping out activities, > which can simply allocate those released pages back. Which seems like > a useless exercise and needless memcpy-s. So I was thinking about > either putting it under config or just removing it (this might be a > harder decision). In embedded (android/bookOS/etc.) there is a daemon, that triggers various zram activities. We can wire in pool-compaction (once under memory pressure), which is a zram sysfs device attribute, instead of pondering zsmalloc with scan callbacks.