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Received: from banye.tbsite.net(mailfrom:qinyuntan@linux.alibaba.com fp:SMTPD_---0XATsvzn_1788778875 cluster:ay36) by smtp.aliyun-inc.com; Mon, 07 Sep 2026 19:01:16 +0800 From: Qinyun Tan To: Andrew Morton Cc: Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , =?UTF-8?q?Michal=20Koutn=C3=BD?= , David Hildenbrand , Zi Yan , Baolin Wang , Usama Arif , Dave Chinner , Qi Zheng , Yosry Ahmed , Nhat Pham , Chengming Zhou , Xunlei Pang , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Qinyun Tan Subject: [PATCH v2 1/4] mm: memcontrol: drop kmemcg_id and use the memcg ID for list_lru indexing Date: Mon, 7 Sep 2026 19:01:08 +0800 Message-ID: <20260907110111.2286932-2-qinyuntan@linux.alibaba.com> X-Mailer: git-send-email 2.43.7 In-Reply-To: <20260907110111.2286932-1-qinyuntan@linux.alibaba.com> References: <20260907110111.2286932-1-qinyuntan@linux.alibaba.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: F17EF80003 X-Stat-Signature: ce16xmqdu9tfx5npkfgcdr1u8fob6og9 X-Rspam-User: X-HE-Tag: 1788778879-158733 X-HE-Meta: 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 PvwxHsKU HfaWX/a/DhWqCFnuswjfwfeDtmVBK9GmxHecuI+sXp6NpjEwgSghDA64A+jvMkLf7QyrNBrjfYIa8OVKWbMveQ/XFx8gbm8YpZjr6QYtSUgg7E84ya6kTOSjZRzGK05dstxLkwHuGm3coBw3lL2051E232mzlZMchm7xABQh/Km7guPekKH3Zb6OSGrxEDicNp3aTuca7QvI8ypDFplLZ5lCj93ndX3y1f99Oc6tNl5jghaiiWx7lgE7+bmTUfWdjrJZ08b+b1Qj/KCatcGeJwqw1JyOavJc3xN39yeajeRgeQU4= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: kmemcg_id is a copy of the memcg ID assigned in memcg_online_kmem(), and is only used as the list_lru xarray index. With cgroup.memory=nokmem the assignment never happens, so every memcg resolves to the per-node lists. The next patch needs the index to work under nokmem as well, so drop the copy and use the memcg ID. The ID works just as well as the copy did: root and NULL still return -1 and use the per-node lists, and the ID is only released after the list_lru reparenting, so a stale or recycled ID can never reach a live list_lru entry. The early return of memcg_offline_kmem() under nokmem is dropped as well, so the reparenting also covers lrus that stay memcg aware without kmem accounting. Signed-off-by: Qinyun Tan --- include/linux/memcontrol.h | 8 +++++--- mm/list_lru.c | 10 +++++----- mm/memcontrol.c | 6 ------ 3 files changed, 10 insertions(+), 14 deletions(-) diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index fdf4812e1d818..edeb287978934 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -254,7 +254,6 @@ struct mem_cgroup { #if BITS_PER_LONG < 64 seqlock_t socket_pressure_seqlock; #endif - int kmemcg_id; #ifdef CONFIG_CGROUP_WRITEBACK struct list_head cgwb_list; @@ -1775,12 +1774,15 @@ static inline void memcg_kmem_uncharge_page(struct page *page, int order) } /* - * A helper for accessing memcg's kmem_id, used for getting + * A helper for accessing the memcg ID, used for getting * corresponding LRU lists. */ static inline int memcg_kmem_id(struct mem_cgroup *memcg) { - return memcg ? memcg->kmemcg_id : -1; + if (!memcg || mem_cgroup_is_root(memcg)) + return -1; + + return memcg->id.id; } struct mem_cgroup *mem_cgroup_from_virt(void *p); diff --git a/mm/list_lru.c b/mm/list_lru.c index a4522ca93ebcb..6fd4e9af84396 100644 --- a/mm/list_lru.c +++ b/mm/list_lru.c @@ -502,7 +502,7 @@ static void memcg_reparent_list_lru_one(struct list_lru *lru, int nid, struct list_lru_one *src, struct mem_cgroup *dst_memcg) { - int dst_idx = dst_memcg->kmemcg_id; + int dst_idx = memcg_kmem_id(dst_memcg); struct list_lru_one *dst; spin_lock_irq(&src->lock); @@ -536,7 +536,7 @@ void memcg_reparent_list_lrus(struct mem_cgroup *memcg, struct mem_cgroup *paren * allocating a new mlru since CSS_DYING is already set for this * memcg a rcu grace period ago. */ - mlru = xa_load(&lru->xa, memcg->kmemcg_id); + mlru = xa_load(&lru->xa, memcg_kmem_id(memcg)); if (!mlru) continue; @@ -551,7 +551,7 @@ void memcg_reparent_list_lrus(struct mem_cgroup *memcg, struct mem_cgroup *paren for_each_node(i) memcg_reparent_list_lru_one(lru, i, &mlru->node[i], parent); - xa_erase_irq(&lru->xa, memcg->kmemcg_id); + xa_erase_irq(&lru->xa, memcg_kmem_id(memcg)); /* * Here all list_lrus corresponding to the cgroup are guaranteed @@ -566,7 +566,7 @@ void memcg_reparent_list_lrus(struct mem_cgroup *memcg, struct mem_cgroup *paren static inline bool memcg_list_lru_allocated(struct mem_cgroup *memcg, struct list_lru *lru) { - int idx = memcg->kmemcg_id; + int idx = memcg_kmem_id(memcg); return idx < 0 || xa_load(&lru->xa, idx); } @@ -602,7 +602,7 @@ static int __memcg_list_lru_alloc(struct mem_cgroup *memcg, if (!mlru) return -ENOMEM; } - xas_set(&xas, pos->kmemcg_id); + xas_set(&xas, memcg_kmem_id(pos)); do { xas_lock_irqsave(&xas, flags); if (!xas_load(&xas) && !css_is_dying(&pos->css)) { diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 7ce50bccf1264..619d4c1f2e8f2 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3780,17 +3780,12 @@ static void memcg_online_kmem(struct mem_cgroup *memcg) return; static_branch_enable(&memcg_kmem_online_key); - - memcg->kmemcg_id = memcg->id.id; } static void memcg_offline_kmem(struct mem_cgroup *memcg) { struct mem_cgroup *parent; - if (mem_cgroup_kmem_disabled()) - return; - if (unlikely(mem_cgroup_is_root(memcg))) return; @@ -4225,7 +4220,6 @@ static struct mem_cgroup *mem_cgroup_alloc(struct mem_cgroup *parent) seqlock_init(&memcg->socket_pressure_seqlock); #endif memcg1_memcg_init(memcg); - memcg->kmemcg_id = -1; #ifdef CONFIG_CGROUP_WRITEBACK INIT_LIST_HEAD(&memcg->cgwb_list); for (i = 0; i < MEMCG_CGWB_FRN_CNT; i++) -- 2.43.7