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[23.128.96.18]) by mx.google.com with ESMTP id h8si18232848jav.8.2021.08.31.08.01.05; Tue, 31 Aug 2021 08:01:23 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@chrisdown.name header.s=google header.b="l6S/pUeA"; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=chrisdown.name Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232858AbhHaM72 (ORCPT + 99 others); Tue, 31 Aug 2021 08:59:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43898 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233366AbhHaM7T (ORCPT ); Tue, 31 Aug 2021 08:59:19 -0400 Received: from mail-wr1-x42d.google.com (mail-wr1-x42d.google.com [IPv6:2a00:1450:4864:20::42d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 994B0C061575 for ; Tue, 31 Aug 2021 05:58:24 -0700 (PDT) Received: by mail-wr1-x42d.google.com with SMTP id t15so21353311wrg.7 for ; Tue, 31 Aug 2021 05:58:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chrisdown.name; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=RlSDoTBJbwZ1+/0ecNtGprCwalpFdAzDsfxdMM/e3GM=; b=l6S/pUeAfrJSprNCOKEOYd0+Fgv9a+ujQ0HxDPG00/VLHsmDx1l+WWWaPEfcR6hOvm vcCJB/kZxW0s+dCeUdJryWsSUpt3N7YnGoU3xfWpBQ8BBRKp2XPW4v5C54TW6+mGqpa6 FgTQX4vh4vrH2Uxa2zZRNnyyZu8u+Hm+JDdoc= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=RlSDoTBJbwZ1+/0ecNtGprCwalpFdAzDsfxdMM/e3GM=; b=KxArDLWU3El6R7Ajp5082N+PFQx5e4rZW4H+k/tuAuczedrnzrVHYRtxqmODKVkxdr bGnhMEc5kT9I7s+u9F9/tFHR8u+IFK26bAg5B1GGTK8G4AwAQ7VvLAhYAzSeGUl/UI9M 87qdOJshnh8orvCwr5VHjeNZh7j+jP07sDDn3aGPCsfB3VbMB4EEPm3qVVzJPKPl/HR3 yyv5Dr3YO7yk239cml9S7jF2KsYbODbVrtNz5GJyWsnucsK6Y+U6468hgW3+H1vN1Geg 9h0YC+NwGEsy3/yLLtMHQaBgolvb5A5TAMW7Fb77lR9l/JUIvzivgyffkNM9nekJREBR 5ALQ== X-Gm-Message-State: AOAM53107Uasg1hCwZfXjBtXbZhfQ0uhyHXVVaq0ge3t3h+bPTgEwbbq yeunbM5XoG23/IKW9Ind/z/GMw== X-Received: by 2002:adf:b743:: with SMTP id n3mr31397338wre.243.1630414702960; Tue, 31 Aug 2021 05:58:22 -0700 (PDT) Received: from localhost ([2620:10d:c093:400::5:bdb8]) by smtp.gmail.com with ESMTPSA id m1sm2590293wmq.10.2021.08.31.05.58.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 31 Aug 2021 05:58:22 -0700 (PDT) Date: Tue, 31 Aug 2021 13:58:21 +0100 From: Chris Down To: Rik van Riel Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, stable@kernel.org, Michal Hocko , Johannes Weiner Subject: Re: [PATCH] mm,vmscan: fix divide by zero in get_scan_count Message-ID: References: <20210826220149.058089c6@imladris.surriel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20210826220149.058089c6@imladris.surriel.com> User-Agent: Mutt/2.1.1 (e2a89abc) (2021-07-12) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Rik van Riel writes: >Changeset f56ce412a59d ("mm: memcontrol: fix occasional OOMs due to >proportional memory.low reclaim") introduced a divide by zero corner >case when oomd is being used in combination with cgroup memory.low >protection. > >When oomd decides to kill a cgroup, it will force the cgroup memory >to be reclaimed after killing the tasks, by writing to the memory.max >file for that cgroup, forcing the remaining page cache and reclaimable >slab to be reclaimed down to zero. > >Previously, on cgroups with some memory.low protection that would result >in the memory being reclaimed down to the memory.low limit, or likely not >at all, having the page cache reclaimed asynchronously later. > >With f56ce412a59d the oomd write to memory.max tries to reclaim all the >way down to zero, which may race with another reclaimer, to the point of >ending up with the divide by zero below. > >This patch implements the obvious fix. > >Fixes: f56ce412a59d ("mm: memcontrol: fix occasional OOMs due to proportional memory.low reclaim") >Signed-off-by: Rik van Riel Thanks, good catch. No strong preference on this vs. max3(), so feel free to keep my ack either way. Acked-by: Chris Down > >diff --git a/mm/vmscan.c b/mm/vmscan.c >index eeae2f6bc532..f1782b816c98 100644 >--- a/mm/vmscan.c >+++ b/mm/vmscan.c >@@ -2592,7 +2592,7 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc, > cgroup_size = max(cgroup_size, protection); > > scan = lruvec_size - lruvec_size * protection / >- cgroup_size; >+ (cgroup_size + 1); > > /* > * Minimally target SWAP_CLUSTER_MAX pages to keep > >