From nobody Sun Sep 7 14:44:18 2025 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 16DD8EB64DA for ; Fri, 21 Jul 2023 01:44:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229863AbjGUBoJ (ORCPT ); Thu, 20 Jul 2023 21:44:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51090 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229450AbjGUBoH (ORCPT ); Thu, 20 Jul 2023 21:44:07 -0400 Received: from bjm7-spam01.kuaishou.com (smtpcn03.kuaishou.com [103.107.217.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A45B8186; Thu, 20 Jul 2023 18:44:05 -0700 (PDT) Received: from bjm7-pm-mail12.kuaishou.com ([172.28.1.94]) by bjm7-spam01.kuaishou.com with ESMTPS id 36L1hd8D011485 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Fri, 21 Jul 2023 09:43:39 +0800 (GMT-8) (envelope-from yangyifei03@kuaishou.com) DKIM-Signature: v=1; a=rsa-sha256; d=kuaishou.com; s=dkim; c=relaxed/relaxed; t=1689903819; h=from:subject:to:date:message-id; bh=WfBeYmQN+HAjcDnQhJBJiepaQUpxGJpfp8LGbLzGAuw=; b=Uaujp7JrVr1HhJ67/IKB8PC6lCzPwguABUa/mYbRzCJlEzSqAEHPT0u5lEaBUcmfYhVglsuMskD zNAu9f2cVSHPRTkK2DKpir1lJq754dPe/xWT7D0VITqwOEDznIdlwlwb4C36JHtvxa6y3QNe7yz8J QjoFX/q8VCAyp35S4jU= Received: from public-bjmt-d51.idcyz.hb1.kwaidc.com (172.28.1.32) by bjm7-pm-mail12.kuaishou.com (172.28.1.94) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1118.20; Fri, 21 Jul 2023 09:43:38 +0800 From: Efly Young To: CC: , , , , , , , Subject: [PATCH] mm:vmscan: fix inaccurate reclaim during proactive reclaim Date: Fri, 21 Jul 2023 09:41:16 +0800 Message-ID: <20230721014116.3388-1-yangyifei03@kuaishou.com> X-Mailer: git-send-email 2.35.1 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Originating-IP: [172.28.1.32] X-ClientProxiedBy: bjxm-pm-mail01.kuaishou.com (172.28.128.1) To bjm7-pm-mail12.kuaishou.com (172.28.1.94) X-DNSRBL: X-MAIL: bjm7-spam01.kuaishou.com 36L1hd8D011485 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Before commit f53af4285d77 ("mm: vmscan: fix extreme overreclaim and swap floods"), proactive reclaim will extreme overreclaim sometimes. But proactive reclaim still inaccurate and some extent overreclaim. Problematic case is easy to construct. Allocate lots of anonymous memory (e.g., 20G) in a memcg, then swapping by writing memory.recalim and there is a certain probability of overreclaim. For example, request 1G by writing memory.reclaim will eventually reclaim 1.7G or other values more than 1G. The reason is that reclaimer may have already reclaimed part of requested memory in one loop, but before adjust sc->nr_to_reclaim in outer loop, call shrink_lruvec() again will still follow the current sc->nr_to_reclaim to work. It will eventually lead to overreclaim. In theory, the amount of reclaimed would be in [request, 2 * request). Reclaimer usually tends to reclaim more than request. But either direct or kswapd reclaim have much smaller nr_to_reclaim targets, so it is less noticeable and not have much impact. Proactive reclaim can usually come in with a larger value, so the error is difficult to ignore. Considering proactive reclaim is usually low frequency, handle the batching into smaller chunks is a better approach. Signed-off-by: Efly Young Suggested-by: Johannes Weiner Acked-by: Johannes Weiner --- mm/memcontrol.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 4b27e24..d36cf88 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -6741,8 +6741,8 @@ static ssize_t memory_reclaim(struct kernfs_open_file= *of, char *buf, lru_add_drain_all(); =20 reclaimed =3D try_to_free_mem_cgroup_pages(memcg, - nr_to_reclaim - nr_reclaimed, - GFP_KERNEL, reclaim_options); + min(nr_to_reclaim - nr_reclaimed, SWAP_CLUSTER_MAX), + GFP_KERNEL, reclaim_options); =20 if (!reclaimed && !nr_retries--) return -EAGAIN; --=20 1.8.3.1