From nobody Sun Dec 14 05:56:50 2025 Received: from mail-pl1-f169.google.com (mail-pl1-f169.google.com [209.85.214.169]) (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 51CFD41C72 for ; Sat, 13 Dec 2025 08:36:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.169 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765615012; cv=none; b=Arb8CnJXXlNSupxdtnmPZsdySqtsbL7HyyrG+urKqkNQXq4HJy9B15i6oxSFmbFj+cuQ+tCofQn7ik8JWqVC1u7bmxGmYHJA46lNo4pZynfn+C5Tv31e1YjQaHrwwIRxIyps3aX6+7qT0w0X2FHt773xrNbm5xIXvuVLP23NfKE= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765615012; c=relaxed/simple; bh=1aHtFCxzlFj60UbiOSTnQLl5bd6h/HQNzRp4YtUr67Y=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=McVq36Q+eZ0FIih7/N97qbnau9MqyhoCvdW2a9z9ACFNzPYVMPUIyTd/tV+aRdynYMfS3aVCscnTNlcGxusxORA51PKbYzXmmjmW6rXBAAkV9dUOVovaqL7JBS1aMEiN7jzAssB/DPs2cUNoLTxeob9H0p8ZDx7Kx12mxgs2kbs= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=AIvGdQdd; arc=none smtp.client-ip=209.85.214.169 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="AIvGdQdd" Received: by mail-pl1-f169.google.com with SMTP id d9443c01a7336-297dd95ffe4so19106735ad.3 for ; Sat, 13 Dec 2025 00:36:50 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1765615009; x=1766219809; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=QUO4Z6t+8bAoOC2zkdCt5oTJYULmp/swr6svAoHv0Bo=; b=AIvGdQddyfc3PHMwtrg7X1kegsG9xUm7Z0BBmjIz4YXpyOF0FyKn6fsUQIEM8remAg HQXvD3TdViPlqAl1/q7cNuGvY8Nsk8opt1KEaV8eJZk12iOFYKMoV70nbdsliGXnUeOW SaGgPL84SUBUBUkHcijrEzw6qj+g2AkkF/ENCGjdYG/EUweT9fR2+PS1LVf3Ez8nBPTX kuHkRKEKtRZX6aSHI2NndQhtyEXVF2977MeJ72B8kzCumMdHjHZ/heSKx7DH1BtAJx3w /I/fYuvkl7LMA/npJ6U2C4CAOXoep4Bi9gZTCQgaxLuYZgyG7foe5Xifzs6tNL5Fl3OT we9Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1765615009; x=1766219809; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-gg:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=QUO4Z6t+8bAoOC2zkdCt5oTJYULmp/swr6svAoHv0Bo=; b=s/qfei1g9AVB48QV/KPwUSgT7yoxDfChef7jZuxszaaLVxQTpAWf0YCvQfEjGV1IZL 7FLYbM1lpOsY6HP61xg4BVm6QVuAfVWk2qA1RXXcpPQ7wb7k7w60GllVZQE3U1ulBiJd NDE2GCoirLLZcg568L5J/LJFxrJ2Hg8ixZfILlPzeGZw4vZqPcIxP2Du9pH8NohUvLoS mNrd1xqtof3MIYWQnVYc85Aox1RwRhtdygvBLLJjIzMkKHcXL8kPnbc6cxvh/lH7zB0H 2g5gAqjLOKHnuMQ35+7QNTSnmQuhwnLvc2xo0dJmlCpEmIbfgvYRCHdTeE8CDMvhRH4F Dbvg== X-Forwarded-Encrypted: i=1; AJvYcCUZh5HbodY62LN2qJhm/ViaEczFmxN5bVredG3ZzGc5jSECKuOG8bsTA/ZJV3dx65dJc/VwxgUFAuyEKcA=@vger.kernel.org X-Gm-Message-State: AOJu0YxPt/33kecPL/iGCnA/yHSFMzef3QPB0fa1rD5b161tHbKd3RbL EbdfUpSAxvHV6BK4PTjSIDKzsE8da527xuLk5YmdJgPfI4eKd2XCYiMq X-Gm-Gg: AY/fxX5ht435PZFMZb3aFcdlYZ76pY2hwrtUP9Y9n9uX97+cSHjk+nil/Z8KWilCaJy WwbN+uI6aMUssXBgXhCue9JEqnUhUP6JxK9S+aRdvuzW9/cTkfhkP2Xa4H1p7d7+IqbkrK8Mi/k A3gIBSTO9K3PBFVWEO3TEd7iwGn/KBvb63aKdO9quNdZt1cFfIsAhcQpC6Pq/D2cxQ3S/rS2wcB bNX8RwH+KmSc1EzdkJaX3s8dA3VCvyCjykuJ2xUTA2ksYQfr0XXFd19e+DU5CCsOELIwFcQFq+l 2Y4dtovLMg1by65eNbB6DbXrQaVQPMZz+CHflMcnhJ53wJ8DVZZqfx44Qa093M3asGR4RMwF+aw Y/1xO/ICXPJL+FZYoCXi9PviZtVPkfSRAyMeHp05DUEWGs4dFfJOLOF3mOt5ocmvnjWgAH/TIU9 Q59ioAH7MqD2lsKg8cI7JmvUsqm+eHEFYomOuXHvR9RAQYYVMFQmMBxdp0+XVr7diVzdM= X-Google-Smtp-Source: AGHT+IF9irKZasWPzWyf4lQTlZvixoJdNYFsprCdE3fzI1IBo3nfOigGTBcKKIDBMGNNA+JEWKK67Q== X-Received: by 2002:a17:902:ef47:b0:298:33c9:eda1 with SMTP id d9443c01a7336-29f24345b37mr37230755ad.43.1765615009519; Sat, 13 Dec 2025 00:36:49 -0800 (PST) Received: from deepanshu-kernel-hacker.. ([2405:201:682f:389d:6d95:e330:61e2:af5f]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-29eea016c86sm76479845ad.54.2025.12.13.00.36.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 13 Dec 2025 00:36:48 -0800 (PST) From: Deepanshu Kartikey To: akpm@linux-foundation.org, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, hannes@cmpxchg.org, david@kernel.org, mhocko@kernel.org, zhengqi.arch@bytedance.com, shakeel.butt@linux.dev, lorenzo.stoakes@oracle.com, yuzhao@google.com, heftig@archlinux.org, oleksandr@natalenko.name, bgeffon@google.com Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Deepanshu Kartikey , syzbot+90fcab4d88cffed6d0d8@syzkaller.appspotmail.com Subject: [PATCH] mm: vmscan: always allow writeback during memcg reclaim Date: Sat, 13 Dec 2025 14:06:39 +0530 Message-ID: <20251213083639.364539-1-kartikey406@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" When laptop_mode is enabled, may_writepage is set to 0 in try_to_free_mem_cgroup_pages(). This triggers a warning in MGLRU's lru_gen_shrink_lruvec(): VM_WARN_ON_ONCE(!sc->may_writepage || !sc->may_unmap); The warning occurs because MGLRU expects full reclaim capabilities to function correctly. The call path is: mem_cgroup_resize_max() try_to_free_mem_cgroup_pages() do_try_to_free_pages() shrink_node() shrink_lruvec() lru_gen_shrink_lruvec() <-- WARNING Unlike kswapd or direct reclaim where laptop_mode's disk-saving behavior is a reasonable optimization, memcg limit enforcement is a hard requirement - memory MUST be freed when a cgroup exceeds its limit. The may_unmap field is already set unconditionally to 1 in this path, acknowledging that memcg reclaim needs full capabilities. Set may_writepage unconditionally to 1 for memcg reclaim to ensure MGLRU works correctly and memory limits are properly enforced. Fixes: bd74fdaea146 ("mm: multi-gen LRU: support page table walks") Reported-by: syzbot+90fcab4d88cffed6d0d8@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3D90fcab4d88cffed6d0d8 Signed-off-by: Deepanshu Kartikey --- Note: Only compile-tested. No reproducer available from syzbot. --- mm/vmscan.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 900c74b6aa62..5e1c99d9cbd7 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -6669,7 +6669,7 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem= _cgroup *memcg, .reclaim_idx =3D MAX_NR_ZONES - 1, .target_mem_cgroup =3D memcg, .priority =3D DEF_PRIORITY, - .may_writepage =3D !laptop_mode, + .may_writepage =3D 1, .may_unmap =3D 1, .may_swap =3D !!(reclaim_options & MEMCG_RECLAIM_MAY_SWAP), .proactive =3D !!(reclaim_options & MEMCG_RECLAIM_PROACTIVE), --=20 2.43.0