From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta1.migadu.com (out-233.mta1.migadu.com [95.215.58.233]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B57E936F8E5 for ; Fri, 28 Aug 2026 09:25:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.233 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787909127; cv=none; b=iqaSrqGns0jMAzYww5GCvTAbxbWNApTzESthRM7Ywm1cmqRz6uZc9z4LZaFeH+W7ieMk6iyFACvg6I2E5GCPMY9kvYJWStubBaBAOPvSVJZbfGexAP7t+QyRe/rL/ZwtCeJM2NdfH7vOyL9IwWJnDc0p8RFKVRvppZIPtg1A6ec= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787909127; c=relaxed/simple; bh=eE7AKtJ5rHDjCHFP0sbjzrcKFX6z6p2ntCRRXg0JHB8=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=e0E9OvAjKnoV9keY7MJofKBgPqGZYkXMWfhuxF0FQ49tNfCM8wWUXwyVsjwg6e0E6TH81c8JUEEPlqt7DqsbdXVMxKOsYnGW1ZQ9Kdwk9cd8wo4yQcXPnQvIzqner0Xd+4dxhud+KZ1dUPcDc7FPjfO+0slXbOHPRlhwFa6/LU8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=qLJlYmEQ; arc=none smtp.client-ip=95.215.58.233 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="qLJlYmEQ" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=eE7AKtJ5rHDjCHFP0sbjzrcKFX6z6p2ntCRRXg0JHB8=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1787909123; v=1; x=1788513923; b=qLJlYmEQsg2nGJ/WAESfsZ/t9JC5CFBWxE2aegEVKi8U8bbevbLb//xflTlm5GQeXfE7XX8T 5XQHjx9bsh3uYTsSO8TuNRk142VfY1KWzZ3Y89MRbduq6e38gvfY6LcZhrB2jfiB+BoN8dbwazT CMElWu1CgruvFk3htBtBNN90= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id ae2bfd24aaee5f26; 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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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