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Mon, 07 Sep 2026 02:55:28 +0000 X-Mizu-Trace-ID: 12f2adc598a284d7 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 v4 2/2] mm/mglru: fix ineffective memory protection for non-kswapd reclaim Date: Mon, 7 Sep 2026 10:54:45 +0800 Message-Id: <20260907025445.1836238-3-ridong.chen@linux.dev> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260907025445.1836238-1-ridong.chen@linux.dev> References: <20260907025445.1836238-1-ridong.chen@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: CBBDB1C0004 X-Stat-Signature: bao4kr8md4otnuhstxmuhz9o5t8hutci X-HE-Tag: 1788749729-420012 X-HE-Meta: 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 KWENkpes 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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 For MGLRU, memory.min/low is not honored during global proactive reclaim (writing to the root memory.reclaim) and global direct reclaim, because these paths shrink memcgs using stale protection (emin/elow). 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 are whatever a previous kswapd run left behind - or zero if kswapd never ran on this node. Relying on a prior kswapd pass is not correct either: a memcg's emin/elow are derived from its ancestors' memory.min/low settings and from children_min_usage, both of which change over time, so emin/elow go stale even after kswapd has run and must be recomputed at the point of reclaim. Introduce mem_cgroup_calculate_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 Reviewed-by: Barry Song Reviewed-by: Johannes Weiner Signed-off-by: Ridong Chen --- include/linux/memcontrol.h | 10 +++++++++ mm/memcontrol.c | 45 ++++++++++++++++++++++++++++++++++++++ mm/vmscan.c | 8 ++++++- 3 files changed, 62 insertions(+), 1 deletion(-) diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index f227348a3f24a..a65a516adc665 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -1885,6 +1885,16 @@ static inline bool memcg_is_dying(struct mem_cgroup *memcg) } #endif /* CONFIG_MEMCG */ +#if defined(CONFIG_MEMCG) && defined(CONFIG_LRU_GEN) +void mem_cgroup_calculate_protection_path(struct mem_cgroup *root, + struct mem_cgroup *memcg); +#else +static inline void mem_cgroup_calculate_protection_path(struct mem_cgroup *root, + struct mem_cgroup *memcg) +{ +} +#endif + #if defined(CONFIG_MEMCG) && defined(CONFIG_ZSWAP) bool obj_cgroup_may_zswap(struct obj_cgroup *objcg); void obj_cgroup_charge_zswap(struct obj_cgroup *objcg, size_t size); diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 256b68ffca70e..ae568fc688130 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -5214,6 +5214,51 @@ 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_calculate_protection_path - compute protection along a 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_calculate_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 b4c9b8f3dfe99..8409ea4bbf379 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -5111,7 +5111,13 @@ 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, mem_cgroup_calculate_protection() has already + * been called during the top-down cgroup traversal. + */ + if (!current_is_kswapd()) + mem_cgroup_calculate_protection_path(NULL, memcg); + if (mem_cgroup_below_min(NULL, memcg)) return MEMCG_LRU_YOUNG; -- 2.34.1