From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id A1905CDE001 for ; Thu, 25 Jun 2026 15:18:02 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 9C3A86B00AE; Thu, 25 Jun 2026 11:18:01 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 99B856B00AF; Thu, 25 Jun 2026 11:18:01 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 88A6A6B00B0; Thu, 25 Jun 2026 11:18:01 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 61BB56B00AE for ; Thu, 25 Jun 2026 11:18:01 -0400 (EDT) Received: from smtpin01.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay07.hostedemail.com (Postfix) with ESMTP id E00AD165D7C for ; Thu, 25 Jun 2026 15:18:00 +0000 (UTC) X-FDA: 84918790320.01.550B778 Received: from out-176.mta1.migadu.com (out-176.mta1.migadu.com [95.215.58.176]) by imf25.hostedemail.com (Postfix) with ESMTP id E7C6FA0007 for ; Thu, 25 Jun 2026 15:17:58 +0000 (UTC) Authentication-Results: imf25.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=araeRisd; spf=pass (imf25.hostedemail.com: domain of qi.zheng@linux.dev designates 95.215.58.176 as permitted sender) smtp.mailfrom=qi.zheng@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1782400679; b=osp4haeo+73P53Q31cLnNvWhaxKpEhoZSkldaDCKig6weGfc2szcihr0pJ9NHJ5Ym8y3fU BnluLeXYUVb+ybm0m0jpfWwhTAdwLQmdIvvABaBaZPqvYyhvm7ia5vyJbKhftjqgsttPJY rFrNaBapyloYtTBjGNVf8PBrnufK44A= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1782400679; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:references:dkim-signature; bh=0abFjDD7MeWR8jXMZ2j0zCKAbj5uTG1W2qlcF8YqFc4=; b=N7N5y+vyHH7YX4X4jV71+ztt5xkmFrZN10xvxcAiPwjrsN32iMRXs95WgvtGjJ6FWH8b4q mZRio8+Fk4Gmn4diWYr9oi9v+VKzYWmK68TS0EmRaLvihxJHRxRG9IlLX/vbN1TXprR5RC xWy8VrSDJOCFiyJvLiui3f8Jw/A1fA4= ARC-Authentication-Results: i=1; imf25.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=araeRisd; spf=pass (imf25.hostedemail.com: domain of qi.zheng@linux.dev designates 95.215.58.176 as permitted sender) smtp.mailfrom=qi.zheng@linux.dev; dmarc=pass (policy=none) header.from=linux.dev 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=1782400676; 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=0abFjDD7MeWR8jXMZ2j0zCKAbj5uTG1W2qlcF8YqFc4=; b=araeRisdZjkkXDB5B5YHuyjgxiM3QgILhTA3HYQM2YO4riqCwXB16muACRB18zccxmj6HB uk5sdyKDreRF+CYXqUsePISuTN1byrhnIsvTqYnq8CpyfVWyZlNIte2FgGzk+V6kjepyj3 1MUTcDj9eg6EsdVDrA1sykzJH9DqGZo= 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 v3] mm: mglru: fix stale batch updates after memcg reparenting Date: Thu, 25 Jun 2026 23:15:54 +0800 Message-ID: <20260625151554.55105-1-qi.zheng@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Stat-Signature: 6y43nwxykj1hsn16eyejgfrds4r5h99g X-Rspamd-Queue-Id: E7C6FA0007 X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1782400678-67344 X-HE-Meta: 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 JZivLN12 iYEmK/3SowGWjdOaxHmEGrXKz1evTKigFoUFoijWk2nGAhmkvYzoUGLdSzP6GnQxet7ejcuOVRet0No2Kv51goyQ+AyZrlyH5YyFf66/9bYFWEC1JilLw8455X8KfM2CBXYxi71Vb7P0/iiCHX8UQGnoHEH1EviiGofB2axv0nxscuHFlE/veTbWGBuo8pdgO1SLkTt2lo5QrrG5Jk0h+1hEbIEWBhyachu3UfX0ZKREj1KMKZqMIrEfbsg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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))); And the user-visible impact of underestimated nr_pages in MGLRU was premature OOMs because MGLRU does not try to reclaim memory when nr_pages reaches zero, but there are still more pages. To fix it, make reset_batch_size() check CSS_DYING under RCU before flushing the pending batch. A non-dying memcg keeps the original lruvec stable against RCU-delayed offlining; a dying memcg redirects the deltas to the first non-dying ancestor. 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 --- Changes in v3: - re-implement lock_batch_lruvec() by checking CSS_DYING under the RCU lock (suggested by Harry) - update the commit message (suggested by Harry) - temporarily drop the previous Reviewed-by tags (since the sync method has changed) - rebase onto the next-20260624 Changes in v2: - update the commit message (pointed by Barry) - collect Reviewed-by mm/vmscan.c | 45 ++++++++++++++++++++++++++++++++++++++------- 1 file changed, 38 insertions(+), 7 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 35c3bb15ae96..1ec8c23c72b9 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -3262,10 +3262,44 @@ 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 pglist_data *pgdat = lruvec_pgdat(lruvec); + struct mem_cgroup *memcg = lruvec_memcg(lruvec); + + rcu_read_lock(); + + /* + * The memcg can be NULL when the memory controller is disabled. + * Otherwise, the caller keeps the memcg owning @lruvec alive. + */ + if (!memcg || !css_is_dying(&memcg->css)) + goto lock; + + do { + memcg = parent_mem_cgroup(memcg); + } while (memcg && css_is_dying(&memcg->css)); + lruvec = mem_cgroup_lruvec(memcg, pgdat); + +lock: + spin_lock_irq(&lruvec->lru_lock); + + 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 +3319,8 @@ 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 +3815,8 @@ 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); @@ -4867,9 +4900,7 @@ 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), -- 2.54.0