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Wed, 26 Aug 2026 13:31:19 +0000 X-Mizu-Trace-ID: 57b289fe451a8707 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 , 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: [RFC PATCH] mm/mglru: fix ineffective memory protection for non-kswapd reclaim Date: Wed, 26 Aug 2026 21:30:54 +0800 Message-Id: <20260826133054.88529-1-ridong.chen@linux.dev> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: D6A011A0011 X-Stat-Signature: 4zhyycr7eut9k6fpi8kg7dueixksanxu X-HE-Tag: 1787751090-302889 X-HE-Meta: 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 71SrI5zP S29iIE3NgllSYWfbCeFqAtNNgrQvk8XPIH5EtkEgqlUVAedbjbRZSMW+NApdQdZb3vk+yaBQZvyrNde8aJGqs3cHWBnKCPqdUPTWLxHpSv6rTfnylKd4+dG5dBbOTe/61CzoFiWx8ZeFUskHuenXM2vKjPuUqF4gTYCrC1kBpEfFBZdK/EvLNhNq+JV5lueZSzXhMxEXXaI23mYQRFkrumpbnn9sr73en1JI9h5DwYHm4+8p2vxUBcqwVeZKUPB8jXgoPraTP8U4bKH348isTdhvh/6hWdClXLXVGO17ZWUBdX3qTE543LOaAxf6fgzn+FxfjS7BJacj/1jCRtaiy8f5vDSgPVTeR7vbhHOHBSzqPQFV21nEwZqx8ZFd0VGmgskyOubG6+y+KR0ZJwPxlk1L6pt/CNExs//SXyxDfd/pV0cSg1J1yGqDJ350IYAgBm8JLq5lFDByNPkRLwe4cPQRwGAqhDnk88BPm0L2jMzOLCu4WUrT9Nja+7roGf6onP7cAJHkYCsO3L6V4cQw3yhCFCl7GzlNOtzaiEVYcmIuZl7knLfk7fDawrKbu9Akf7chGC/Y/gbfYUAGqYrVSH7ISR+C3VQa4SKhX/A8t4a9n/t2CIj02r8I1t/3tGTPPrhlPVvnisy5H/aTCT1JHiRF15ZW/DgGL8lsPsAQZZKhbVU+Kf5N/0cqQ2HKS6BjDZSk0bVGnV2lwJEOXAMVvGTd1et5ANDREEQ3r3PEtqHsIypYlJ4xylkQhTwj+shoTRNTj 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 Signed-off-by: Ridong Chen --- include/linux/memcontrol.h | 7 +++++++ mm/memcontrol.c | 42 ++++++++++++++++++++++++++++++++++++++ mm/vmscan.c | 8 +++++++- 3 files changed, 56 insertions(+), 1 deletion(-) diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 7d1c0ce189a8..26be8277d64b 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -605,6 +605,8 @@ static inline void mem_cgroup_protection(struct mem_cgroup *root, void mem_cgroup_calculate_protection(struct mem_cgroup *root, struct mem_cgroup *memcg); +void mem_cgroup_protection_path(struct mem_cgroup *root, + struct mem_cgroup *memcg); static inline bool mem_cgroup_unprotected(struct mem_cgroup *target, struct mem_cgroup *memcg) @@ -1133,6 +1135,11 @@ static inline void mem_cgroup_calculate_protection(struct mem_cgroup *root, { } +static inline void mem_cgroup_protection_path(struct mem_cgroup *root, + struct mem_cgroup *memcg) +{ +} + 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..c739db33b917 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -5198,6 +5198,48 @@ void mem_cgroup_calculate_protection(struct mem_cgroup *root, page_counter_calculate_protection(&root->memory, &memcg->memory, recursive_protection); } +/** + * 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(); +} + 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 6dff207ad8c6..e572d2742c8c 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