From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-181.mta0.migadu.com (out-181.mta0.migadu.com [91.218.175.181]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 939FB23BD06 for ; Tue, 23 Jun 2026 02:44:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.181 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782182674; cv=none; b=MqTGYWLzv9kUb+3ChjL+lhahmGhtCyouT+tUKdRWgsQnNmdsNJW9LOLPV9/Me+9JgU/WlnDXwUymHeCTTmXnbiMLjMh41fSrbtt2AU1dnpSTOb1etdFI8nlySn3nmjMgnBLTyBZwP7blvgKmW69t6bF6Rw4zLS+/yNApnpJD8lA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782182674; c=relaxed/simple; bh=M4cTZOsUtp3cYswHivr9vnJI0i1A+C1YgFKpFVlh9PQ=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=vCrsuA0h2WkJ4hIzfxdi0V8LdxS3mWPfUlmcWC0yBCMDzwbrJ/yknX7bucCn5uepnU/kelQ7a/J5+ZAfdCPXU8WQExC8oDL3naCtIuNp2LsuK/RqS6/vry3BOky1Su5u2LowVKTZpIcuGOQn/GqPmUawyLudDZ7waVM1WWG8V+0= 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=PJaN6uT9; arc=none smtp.client-ip=91.218.175.181 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="PJaN6uT9" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1782182670; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=a8+eeytXWCIVLCbNBOynGcBvbUA5M39lvYGkiNnFZO8=; b=PJaN6uT9J5NDYZoml3Hbdmj+s929N+ngw8MxLLg7VrG/3KFVLHJ00nBb8oVd4Pevs3i3WX DmnWEBkUt16AaqT/66s8Nw9kMBzMCS9/jybeucwFcjVSWTmkVRDi5Q92oib9s2Ma5zrafi dFJfp1wUHfx4vfdPehzulUYLwsoDnyQ= From: Qi Zheng To: akpm@linux-foundation.org, david@kernel.org, kasong@tencent.com, shakeel.butt@linux.dev, baohua@kernel.org, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, hannes@cmpxchg.org, harry@kernel.org, muchun.song@linux.dev, peiyang_he@smail.nju.edu.cn, mhocko@kernel.org, roman.gushchin@linux.dev, ljs@kernel.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Qi Zheng , stable@vger.kernel.org Subject: [PATCH v2] mm: mglru: fix stale batch updates after memcg reparenting Date: Tue, 23 Jun 2026 10:42:37 +0800 Message-ID: <20260623024237.45990-1-qi.zheng@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 X-Migadu-Flow: FLOW_OUT From: Qi Zheng The mglru page table walker batches per-generation size deltas in walk->nr_pages while walking page tables without holding the lruvec lock. The reset_batch_size() later folds those deltas into walk->lruvec under the lruvec lock. The page table walker can run concurrently with the memcg reparenting path as follows: CPU0 CPU1 ==== ==== walk_mm --> walk_page_range --> update_batch_size --> walk->nr_pages += delta mem_cgroup_css_offline --> memcg_reparent_objcgs --> lock lruvec lru_gen_reparent_memcg --> reparent child folios to parent unlock lruvec lock lruvec reset_batch_size --> child lrugen->nr_pages += delta This will trigger the following warning in lru_gen_exit_memcg(): VM_WARN_ON_ONCE(memchr_inv(lruvec->lrugen.nr_pages, 0, sizeof(lruvec->lrugen.nr_pages))); To fix it, add lrugen->reparented to remember the new owner of a reparented lruvec, and make reset_batch_size() charge pending deltas to that owner. Reported-by: Peiyang He Closes: https://lore.kernel.org/all/5A9E929D82717101+12fcf643-efb8-4b9a-a53a-1e28cc894f0b@smail.nju.edu.cn Fixes: f304652609ea ("mm: vmscan: prepare for reparenting MGLRU folios") Cc: Signed-off-by: Qi Zheng Reviewed-by: Barry Song --- include/linux/mmzone.h | 4 ++++ mm/vmscan.c | 43 +++++++++++++++++++++++++++++++++++------- 2 files changed, 40 insertions(+), 7 deletions(-) diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index ca2712187147..0d572db2ef64 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -584,6 +584,10 @@ struct lru_gen_folio { u8 gen; /* the list segment this lru_gen_folio belongs to */ u8 seg; +#ifdef CONFIG_MEMCG + /* the lruvec this lruvec has been reparented to */ + struct lruvec *reparented; +#endif /* per-node lru_gen_folio list for global reclaim */ struct hlist_nulls_node list; }; diff --git a/mm/vmscan.c b/mm/vmscan.c index 35c3bb15ae96..64362cbed814 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -3262,10 +3262,37 @@ static void update_batch_size(struct lru_gen_mm_walk *walk, struct folio *folio, walk->nr_pages[new_gen][type][zone] += delta; } +#ifdef CONFIG_MEMCG +static struct lruvec *lock_batch_lruvec(struct lruvec *lruvec) +{ + struct lruvec *reparented; + + for (;;) { + lruvec_lock_irq(lruvec); + + reparented = lruvec->lrugen.reparented; + if (!reparented) + break; + + lruvec_unlock_irq(lruvec); + lruvec = reparented; + } + + return lruvec; +} +#else +static struct lruvec *lock_batch_lruvec(struct lruvec *lruvec) +{ + lruvec_lock_irq(lruvec); + + return lruvec; +} +#endif + static void reset_batch_size(struct lru_gen_mm_walk *walk) { int gen, type, zone; - struct lruvec *lruvec = walk->lruvec; + struct lruvec *lruvec = lock_batch_lruvec(walk->lruvec); struct lru_gen_folio *lrugen = &lruvec->lrugen; walk->batched = 0; @@ -3285,6 +3312,8 @@ static void reset_batch_size(struct lru_gen_mm_walk *walk) lru += LRU_ACTIVE; __update_lru_size(lruvec, lru, zone, delta); } + + lruvec_unlock_irq(lruvec); } static int should_skip_vma(unsigned long start, unsigned long end, struct mm_walk *args) @@ -3779,11 +3808,8 @@ static void walk_mm(struct mm_struct *mm, struct lru_gen_mm_walk *walk) mmap_read_unlock(mm); } - if (walk->batched) { - lruvec_lock_irq(lruvec); + if (walk->batched) reset_batch_size(walk); - lruvec_unlock_irq(lruvec); - } cond_resched(); } while (err == -EAGAIN); @@ -4563,6 +4589,8 @@ void lru_gen_reparent_memcg(struct mem_cgroup *memcg, struct mem_cgroup *parent, mem_cgroup_update_lru_size(parent_lruvec, lru, zid, size); } } + + child_lruvec->lrugen.reparented = parent_lruvec; } #endif /* CONFIG_MEMCG */ @@ -4867,9 +4895,7 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec, walk = current->reclaim_state->mm_walk; if (walk && walk->batched) { walk->lruvec = lruvec; - lruvec_lock_irq(lruvec); reset_batch_size(walk); - lruvec_unlock_irq(lruvec); } mod_lruvec_state(lruvec, PGDEMOTE_KSWAPD + reclaimer_offset(sc), @@ -5784,6 +5810,9 @@ void lru_gen_init_lruvec(struct lruvec *lruvec) lrugen->max_seq = MIN_NR_GENS + 1; lrugen->enabled = lru_gen_enabled(); +#ifdef CONFIG_MEMCG + lrugen->reparented = NULL; +#endif for (i = 0; i <= MIN_NR_GENS + 1; i++) lrugen->timestamps[i] = jiffies; -- 2.54.0