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Thu, 18 Dec 2025 06:06:51 -0800 (PST) Received: from localhost ([2603:7000:c01:2716:929a:4aff:fe16:c778]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8beeb5f2911sm168014685a.17.2025.12.18.06.06.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 18 Dec 2025 06:06:49 -0800 (PST) Date: Thu, 18 Dec 2025 09:06:45 -0500 From: Johannes Weiner To: Qi Zheng Cc: hughd@google.com, mhocko@suse.com, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, david@kernel.org, lorenzo.stoakes@oracle.com, ziy@nvidia.com, harry.yoo@oracle.com, imran.f.khan@oracle.com, kamalesh.babulal@oracle.com, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, chenridong@huaweicloud.com, mkoutny@suse.com, akpm@linux-foundation.org, hamzamahfooz@linux.microsoft.com, apais@linux.microsoft.com, lance.yang@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Muchun Song , Qi Zheng Subject: Re: [PATCH v2 27/28] mm: memcontrol: eliminate the problem of dying memory cgroup for LRU folios Message-ID: References: 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: 7AED5140007 X-Stat-Signature: fimc8wgrwha34g883sug5zmqhchwwsk6 X-Rspam-User: X-HE-Tag: 1766066812-745949 X-HE-Meta: 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 7kZjJqEh 0kS7qizVOCse2vSOhj20vvoiNU5kY5xanak3l0AdARquIUSxuExTQ3DXtnQIa+Q7wIzPX9PAwXkUhJKMsZzXgVo8LVuxNawQ0qRAJbnXGBmSnO5lw3unyz6oRlK3+T1jT9iC8UbzM54enH4//HfbyZJhHYU9gfga/MV0065VtfKOeA/5Pm1i0j6jbVnKnrHq7LvUCsbbtSe9OKGS/X3AzMi4KoPEXeHQgTMUUyl+KYRfqmB+QTV/jXYb+NX8WMZaLCRZhns/8cCgJDh/KD13z4o3JfHjxj/O+kBeu1FJeAwSZRn/20jaSvb+PqfrQvy2KVtEbzkCJlbG4K03jjouXR226Yik9J/68UbXoeXW0zy6O6+e71qLZUyyO+OujXpgeEOEj3ws49WU+FzcsoIXxt0AX9V9w0KLXqXZrswrw8KkBxhI= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Dec 17, 2025 at 03:27:51PM +0800, Qi Zheng wrote: > From: Muchun Song > > Pagecache pages are charged at allocation time and hold a reference > to the original memory cgroup until reclaimed. Depending on memory > pressure, page sharing patterns between different cgroups and cgroup > creation/destruction rates, many dying memory cgroups can be pinned > by pagecache pages, reducing page reclaim efficiency and wasting > memory. Converting LRU folios and most other raw memory cgroup pins > to the object cgroup direction can fix this long-living problem. This is already in the coverletter. Please describe here what the patch itself does. IOW, now that everything is set up, switch folio->memcg_data pointers to objcgs, update the accessors, and execute reparenting on cgroup death. > Finally, folio->memcg_data of LRU folios and kmem folios will always > point to an object cgroup pointer. The folio->memcg_data of slab > folios will point to an vector of object cgroups. > @@ -223,22 +223,55 @@ static inline void __memcg_reparent_objcgs(struct mem_cgroup *src, > > static inline void reparent_locks(struct mem_cgroup *src, struct mem_cgroup *dst) > { > + int nid, nest = 0; > + > spin_lock_irq(&objcg_lock); > + for_each_node(nid) { > + spin_lock_nested(&mem_cgroup_lruvec(src, > + NODE_DATA(nid))->lru_lock, nest++); > + spin_lock_nested(&mem_cgroup_lruvec(dst, > + NODE_DATA(nid))->lru_lock, nest++); > + } > } Looks okay to me. If this should turn out to be a scalability problem in practice, we can make objcgs per-node, and then reparent lru/objcg pairs on a per-node basis without nesting locks. > static inline void reparent_unlocks(struct mem_cgroup *src, struct mem_cgroup *dst) > { > + int nid; > + > + for_each_node(nid) { > + spin_unlock(&mem_cgroup_lruvec(dst, NODE_DATA(nid))->lru_lock); > + spin_unlock(&mem_cgroup_lruvec(src, NODE_DATA(nid))->lru_lock); > + } > spin_unlock_irq(&objcg_lock); > } > > +static void memcg_reparent_lru_folios(struct mem_cgroup *src, > + struct mem_cgroup *dst) > +{ > + if (lru_gen_enabled()) > + lru_gen_reparent_memcg(src, dst); > + else > + lru_reparent_memcg(src, dst); > +} > + > static void memcg_reparent_objcgs(struct mem_cgroup *src) > { > struct obj_cgroup *objcg = rcu_dereference_protected(src->objcg, true); > struct mem_cgroup *dst = parent_mem_cgroup(src); > > +retry: > + if (lru_gen_enabled()) > + max_lru_gen_memcg(dst); > + > reparent_locks(src, dst); > + if (lru_gen_enabled() && !recheck_lru_gen_max_memcg(dst)) { > + reparent_unlocks(src, dst); > + cond_resched(); > + goto retry; > + } > > __memcg_reparent_objcgs(src, dst); > + memcg_reparent_lru_folios(src, dst); Please inline memcg_reparent_lru_folios() here, to keep the lru vs lrugen switching as "flat" as possible: if (lru_gen_enabled()) { if (!recheck_lru_gen_max_memcgs(parent)) { reparent_unlocks(memcg, parent); cond_resched(); goto retry; } lru_gen_reparent_memcg(memcg, parent); } else { lru_reparent_memcg(memcg, parent); } > @@ -989,6 +1022,8 @@ struct mem_cgroup *get_mem_cgroup_from_current(void) > /** > * get_mem_cgroup_from_folio - Obtain a reference on a given folio's memcg. > * @folio: folio from which memcg should be extracted. > + * > + * The folio and objcg or memcg binding rules can refer to folio_memcg(). See folio_memcg() for folio->objcg/memcg binding rules.