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[173.79.60.52]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-5367b3d1ccbsm12827051cf.0.2026.10.19.09.10.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 19 Oct 2026 09:10:42 -0700 (PDT) Date: Mon, 19 Oct 2026 12:10:40 -0400 From: Gregory Price To: Li Zhe Cc: akpm@linux-foundation.org, david@kernel.org, ziy@nvidia.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, ying.huang@linux.alibaba.com, ljs@kernel.org, mhocko@suse.com, muchun.song@linux.dev, roman.gushchin@linux.dev, shakeel.butt@linux.dev, weixugc@google.com, cgroups@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [RFC 0/2] mm: add source selectors to memory.reclaim Message-ID: References: <20261019141401.11927-1-lizhe.67@bytedance.com> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261019141401.11927-1-lizhe.67@bytedance.com> X-Rspamd-Queue-Id: 2973916000B X-Stat-Signature: b9tb7t43o6tibiqqochtru97cifrpsbh X-Rspamd-Server: rspam06 X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_BLOCKED,RCVD_IN_ZEN_BLOCKED_OPENDNS, SPF_HELO_PASS,SPF_PASS autolearn=no autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1792426243-283300 X-HE-Meta: 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 BSbzncvN S3Wnf97tRIPq76IJqBDDi187hWdB5Ktv/54jaS6m19wI4ucSs3nQY4gCLO9WlP5s+xu11Ehe9xvo8I6Jmu/x9yd2M+YmGo2jmt6Z/u4Cn1zMUGirjH1uT0ctZTWDWyV24Lb7P0NhDObUAJ9wd5Ojd7eA834w6QUIBFKpGlngvX1ab/gurpJYN9tq7iRi7U1MKTM/VwOxBxSpYNACFfEEPxlvkSPsxC+MxMR+VUjTd77gE+sBPviqr3vO8A6qL2htx82oZu+aaK/rAfh7nCanuRKYDebv4zHTExmjaQShiJxpolTiwLPa5ZvmNQ1LNTETmTTILX+CEsE94Lcxh6yASrKmSuFrvdoNJy/iOdyVQbvKB/mFDxoIqX4WoEOxkx731fZ2a12RKoesti1TdOnVk6bnlLg== 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 Mon, Oct 19, 2026 at 10:13:59PM +0800, Li Zhe wrote: > memory.reclaim is a useful proactive reclaim interface for memcgs, but > tiered memory makes "reclaim N bytes from this memcg" underspecified for > userspace controllers that manage memory placement across tiers. The > kernel's reclaim policy is aging-based, and on tiered systems aging may > demote folios before they are eventually evicted. Without a way to > declare where reclaim pressure should start, userspace can only reclaim > from the memcg as a whole and observe one aggregate progress value. This is not a good argument for pushing the complexity of managing tiers into userspace - it is an argument for fixing the reclaim interface to handle demotion and eviction sanely - which presently we do not do. My best examples: 1) the watermarks don't make sense for lower tiers that need to absorb large amounts of demotions from upper tiers. It's likely lower tiers need larger WMARK_PROMO to let low-tier kswapd run longer. 2) proactive and async reclaim current reclaim top-down, which results in swapping directly from top-tiers because lower tiers don't have space to absorb demotions. We should experiment with async / proactive reclaim applying bottom-up (lowest tier first) so aging the top-tiers demotes into lower tiers more successfully. direct reclaim should stay top-down because we want the best page with the least work to minimize stalls. I have a strong suspicion if we made these change, then memcg.reclaim would work more or less the way you'd want - and anything else can be managed more directly with madvise/process_madvise. I also have concerns with extending memory.reclaim this way permanently locking in reclaim implementation details that prevent us from making changes like this in the future. ~Gregory