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Fri, 28 Aug 2026 09:25:22 +0000 X-Mizu-Trace-ID: ae2bfd24aaee5f26 X-Migadu-Flow: FLOW_OUT From: Ridong Chen To: Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Andrew Morton Cc: Muchun Song , David Hildenbrand , Qi Zheng , Lorenzo Stoakes , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Chris Down , Tejun Heo , Yu Zhao , cgroups@vger.kernel.org (open list:CONTROL GROUP - MEMORY RESOURCE CONTROLLER (MEMCG)), linux-mm@kvack.org (open list:CONTROL GROUP - MEMORY RESOURCE CONTROLLER (MEMCG)), linux-kernel@vger.kernel.org, Ridong Chen , Ridong Chen , stable@vger.kernel.org Subject: [PATCH 2/2] mm/mglru: fix ineffective memory protection for non-kswapd reclaim Date: Fri, 28 Aug 2026 17:24:32 +0800 Message-Id: <20260828092432.1257917-3-ridong.chen@linux.dev> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260828092432.1257917-1-ridong.chen@linux.dev> References: <20260828092432.1257917-1-ridong.chen@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: ztsmp9m6frs69qugycprks1hsgshbq7x X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 94F871C0003 X-Rspam-User: X-HE-Tag: 1787909124-843751 X-HE-Meta: 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 T8U0Qhys 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Ridong Chen memory.min/low is silently bypassed for MGLRU during global proactive reclaim (writing to the root memory.reclaim) and global direct reclaim. It can be reproduced as follows: # echo 7 > /sys/kernel/mm/lru_gen/enabled # cd /sys/fs/cgroup # mkdir -p a/b # echo 100M > a/memory.min # echo +memory > a/cgroup.subtree_control # echo 100M > a/b/memory.min # echo $$ > a/b/cgroup.procs # dd if=/dev/zero of=/tmp/testfile bs=1M count=200 # cat a/b/memory.current 222650368 # echo 500M > memory.reclaim -bash: echo: write error: Resource temporarily unavailable # cat a/b/memory.current 6070272 memory.min is 100M, yet reclaim drops a/b down to 6M, breaking the protection. The traditional LRU path is not affected because shrink_node() calls mem_cgroup_calculate_protection() for each memcg it visits during a top-down tree walk. Commit 30d77b7eef01 ("mm/mglru: fix ineffective protection calculation") moved the protection computation into lru_gen_age_node(), which only runs for kswapd. Non-kswapd global reclaim reaches shrink_one() through lru_gen_shrink_node() -> shrink_many() without any protection computation, so emin/elow remain stale or zero. Introduce mem_cgroup_protection_path() which computes emin/elow along the root-to-target path only by iterating through the cgroup ancestors array top-down. This avoids the full tree traversal that would be needed with mem_cgroup_calculate_protection(), limiting the cost to O(depth) per memcg - typically 3-5 levels. Call it from shrink_one() for the non-kswapd path so that each memcg about to be shrunk has correct protection values. Fixes: e4dde56cd208 ("mm: multi-gen LRU: per-node lru_gen_folio lists") Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Ridong Chen --- include/linux/memcontrol.h | 11 ++++++++++ mm/memcontrol.c | 45 ++++++++++++++++++++++++++++++++++++++ mm/vmscan.c | 8 ++++++- 3 files changed, 63 insertions(+), 1 deletion(-) diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 7d1c0ce189a8..8066b798a759 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -605,6 +605,10 @@ static inline void mem_cgroup_protection(struct mem_cgroup *root, void mem_cgroup_calculate_protection(struct mem_cgroup *root, struct mem_cgroup *memcg); +#ifdef CONFIG_LRU_GEN +void mem_cgroup_protection_path(struct mem_cgroup *root, + struct mem_cgroup *memcg); +#endif static inline bool mem_cgroup_unprotected(struct mem_cgroup *target, struct mem_cgroup *memcg) @@ -1133,6 +1137,13 @@ static inline void mem_cgroup_calculate_protection(struct mem_cgroup *root, { } +#ifdef CONFIG_LRU_GEN +static inline void mem_cgroup_protection_path(struct mem_cgroup *root, + struct mem_cgroup *memcg) +{ +} +#endif + static inline bool mem_cgroup_unprotected(struct mem_cgroup *target, struct mem_cgroup *memcg) { diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 1271d390b617..095050d4296a 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -5198,6 +5198,51 @@ void mem_cgroup_calculate_protection(struct mem_cgroup *root, page_counter_calculate_protection(&root->memory, &memcg->memory, recursive_protection); } +#ifdef CONFIG_LRU_GEN +/** + * mem_cgroup_protection_path - compute protection along root->memcg path + * @root: the top ancestor of the sub-tree being checked (NULL for root_mem_cgroup) + * @memcg: the target memory cgroup + * + * Walk the ancestor path from @root down to @memcg and compute the effective + * protection at each level. This is safe for isolated queries because it + * ensures parents are computed before children. + */ +void mem_cgroup_protection_path(struct mem_cgroup *root, + struct mem_cgroup *memcg) +{ + bool recursive_protection = + cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_RECURSIVE_PROT; + struct cgroup *cg; + int root_level, i; + + if (mem_cgroup_disabled()) + return; + + if (!root) + root = root_mem_cgroup; + + if (memcg == root) + return; + + root_level = root->css.cgroup->level; + cg = memcg->css.cgroup; + + rcu_read_lock(); + for (i = root_level + 1; i <= cg->level; i++) { + struct mem_cgroup *cur; + + cur = mem_cgroup_from_css(cgroup_css(cg->ancestors[i], + &memory_cgrp_subsys)); + if (cur) + page_counter_calculate_protection(&root->memory, + &cur->memory, + recursive_protection); + } + rcu_read_unlock(); +} +#endif /* CONFIG_LRU_GEN */ + static int charge_memcg(struct folio *folio, struct mem_cgroup *memcg, gfp_t gfp) { diff --git a/mm/vmscan.c b/mm/vmscan.c index f11491ee9ed5..e0ba68ede745 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -5102,7 +5102,13 @@ static int shrink_one(struct lruvec *lruvec, struct scan_control *sc) struct mem_cgroup *memcg = lruvec_memcg(lruvec); struct pglist_data *pgdat = lruvec_pgdat(lruvec); - /* lru_gen_age_node() called mem_cgroup_calculate_protection() */ + /* + * For kswapd, lru_gen_age_node() has already called + * mem_cgroup_calculate_protection() + */ + if (!current_is_kswapd()) + mem_cgroup_protection_path(NULL, memcg); + if (mem_cgroup_below_min(NULL, memcg)) return MEMCG_LRU_YOUNG; -- 2.34.1