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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jiayuan Chen , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/vmscan: clear hopeless kswapd when global direct reclaim makes progress Message-Id: <20260709202247.8cf6d7ab840f3a45c7eac409@linux-foundation.org> In-Reply-To: <20260710024429.70923-1-ahacigu.linux@gmail.com> References: <20260710024429.70923-1-ahacigu.linux@gmail.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Stat-Signature: ga4ewq4c5qod48wkzg7eoktf5ty556rs X-Rspamd-Queue-Id: B6E0E1C0003 X-Rspam-User: X-Rspamd-Server: rspam07 X-HE-Tag: 1783653769-588765 X-HE-Meta: U2FsdGVkX18dd2QV3xDC/tdAp8apj1oHcAuF/7m2Zl0lfnHiP6eGvSpEZbp1heVAfAnm/25bKvJ8c08BAky0H7b4gAB0DFNutcnJ6vXm87xTGnAPq3Jkd7Bu9/A10IG67M5fAgTRhpU1lFXK2hjcaOZWlLe21LUHbNiQpiIk6G/5FsS3OPsbA7pMu3mj8saEo+w/6wtxu0qG4i6aSI9XUnoKhzyarUaQIPSY4LGrpsHCUerTVSSt4zruPOwj23WxcmOpqQF+7Bm5x3oUppYmMJX86m9OaUWgWzwa5hgks1qMofJzhOwdE9qsr05OvJv7EC/B2ZnBN4mcWeo0mhqeXGgloq9tA4UgonpVofk6zp4AiyFgiupHq5L2zfmBkFC+PS9baYkyC6aGKypvcIgFCGZX9c73WWcjc4XJpJ2JZkc4pjFLICEbackKJoqRtH8VI4OhNgbB+CW1vPAyTxXxvjELd+arnsKulg4zdArVjqdmpvsKVmXEMT80X5nIdSqk3gqjl8drwj71w9sOP/rX7M4asGX8IYPp2W+MuCkY/USv5Dw1NQir/2E+1t5i+HTtVZBN5PVyanlM9aHExosMSCWy5klrilOeBLozKDnf+gdIpqIeYKTSly2z5iiUYziw8mqCc6hfpZW1AdMuNeokY28MHy322eyeJAXcD7rbLpzey5d1zjXsbFxvcFNtaJ3cQD+vwJEysMgBKUh0ZxbrtLkBMO/KaB8t7Q4Fuj9TPW5sXqlYR26KqOfizlZP+nVwl2IK8/JP49VpYfyLQQmHYMGjpQlOGjgVW/6HK7ncjdNIBmnL6JqgAb5C8VW8fy7FPwzeZGxnZl3Wwnt+mJhyXkT2F//PHrAWmQYUTHmMyIUh8apM5K+t19DXHDWRs3RyYJC/6jVMp3A934yHI1EYdcogoinWtOpYijWY9b5SMBRVlMvaGWW/lMUmx6qn3SE8v8xv8jxP1LEorcmiquZ Hv6ut3Iy 811paz0b8lm7IL4E++PF0nDRjcARZuQA9ctomWrDbYZGJ3LRKmp0bIeuU+tl865g9WG4XHI4pzG0ZWz65dkqGkkqliqcqmxM1gNQmzgi9EWsMh63+tj4sClTJC0XUTA37uLAMuHICZHp8LCtIOy/xWFFWjhCdY922HE2RqeMG7TcG0lwkOnBmlcxfLC6LUbn/1fr6/5zr6d8H4/t72S/529aBzvC0CV3zbuLeOeDX3O0dmaA5TRGankgdNy8mPT1PBLNKrgb6Z1OUAPhAEZ92yYjcdA1bGUR957bTarWCesVE/Q9YIrHItz68A9lt4A/eNv9/DPyOkfRMqFs4FkykjHPMdclJcd2CSR/d Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 9 Jul 2026 19:44:29 -0700 Altan Hacigumus wrote: > Direct reclaim clears the hopeless kswapd state only once the node > becomes balanced. This avoids cgroup memory.high reclaim repeatedly > reviving a kswapd that cannot balance the node. > > However, it also prevents global direct reclaim from reviving kswapd. > Under sustained memory pressure, global direct reclaim may continue > making progress without the node ever reaching the high watermark, > leaving reclaim to allocating tasks. > > Unlike memcg reclaim, global direct reclaim follows the same node-wide > reclaim path as kswapd. Clear the hopeless state when global direct > reclaim makes progress, while continuing to require a balanced node for > memcg reclaim. kswapd_try_clear_hopeless() becomes static since struct > scan_control is private to vmscan.c. > > On a workload with most memory mlocked and the remainder under sustained > churn, with swap enabled, comparing the same 60s window: > base patched > allocstall (all zones) 413441 6532 > pgsteal_direct 15889552 255619 > pgsteal_kswapd 0 26079382 > PSI memory full avg60 13.10% 9.37% > > Direct reclaim was already reclaiming many pages in the baseline; > this change lets kswapd resume doing that work asynchronously. Does this change have any user-visible effect? If so, please describe in elaborate detail. If not then that's OK - we make such changes all the time, but they're less fun.