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[109.81.92.28]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-43d1e4d282esm64612996f8f.18.2026.04.09.00.06.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 09 Apr 2026 00:06:09 -0700 (PDT) Date: Thu, 9 Apr 2026 09:06:08 +0200 From: Michal Hocko To: Kefeng Wang Cc: Andrew Morton , David Hildenbrand , Christian Brauner , Alexander Viro , "Matthew Wilcox (Oracle)" , Jan Kara , "Liam R. Howlett" , Lorenzo Stoakes , Mike Rapoport , Suren Baghdasaryan , Vlastimil Babka , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH RFC] fs: drop_caches: introduce per-node drop_caches interface Message-ID: References: <20260409063503.3475420-1-wangkefeng.wang@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260409063503.3475420-1-wangkefeng.wang@huawei.com> X-Rspam-User: X-Stat-Signature: n953efacyc3h33jia3is57ziccbdrn83 X-Rspamd-Queue-Id: 24BB7C0006 X-Rspamd-Server: rspam09 X-HE-Tag: 1775718371-14177 X-HE-Meta: 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 JFT6cgdy OnFYYwBrDc5De8GO7P6OM0BoS8M6NMtzJkcu5ls2C57mbA3MaH1njVifVNmp1aqqdbfP4gGO98VXOYlMsGDYBbNBao79deRerVfH5Zlie0elzPRoEurvRlTphS3lblbJ1yVSDUkXX2FZhsiPrm8nB02ayVE1wAW2tNZ15+S6FJ+e9qupsm28C/zJvtWQQUEh53hM+Pxh5lP9vxFSPu3oQP/DeNXIKzj3fcb1ZbR2cDVqAXyA0usxNrB4+VwDLPYLGPBvU6u+1T3xKkfb4y63R57tFQmSVH4mqfbUqj/2Rcnp8nsqyiFmta7eQXaJvLIU7xXHg6eScze5yNeDMMHYavt+qFl6fbDE+4IU0bihJiO9WS7nRbx8lIXH8MK0tBkT1pHEiToIefNCtZkzahYpqFb4kpQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu 09-04-26 14:35:03, Kefeng Wang wrote: > Add a sysfs interface at /sys/devices/system/node/nodeX/drop_caches > to allow dropping caches on a specific NUMA node. > > The existing global drop_caches mechanism (/proc/sys/vm/drop_caches) > operates across all NUMA nodes indiscriminately, causing, > - Unnecessary eviction of hot cache on some nodes > - Performance degradation for applications with NUMA affinity > - Long times spent on large systems with lots of memory > > By exposing a per-node interface, admistrator can, > - Target specific nodes experiencing memory pressure > - Preserve cache on unaffected nodes > - Perform reclamation with finer granularity Quite honestly drop_caches is not the best interface to build any new functionality on top of. It has backfired a lot in the past and we have tried to make it extra clear that this should be used for debugging purposes only. Extending it further sounds like a bad step. > One use cases is hot-pluggable NUMA nodes, during hot-remove, simply > dropping pagecache is far more efficient than migrating large amounts > of pages to other nodes, which also eliminating the risk of accessing > potentially faulty memory. Does the per-node reclaim interface can help with this by any means? -- Michal Hocko SUSE Labs