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 X-Spam-Level: X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 28DA4C432BE for ; Tue, 31 Aug 2021 09:59:13 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id BD03A60525 for ; Tue, 31 Aug 2021 09:59:12 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org BD03A60525 Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id 4C7EA6B0071; 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Tue, 31 Aug 2021 09:59:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1630403950; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=WiP8R2FARUsYFRgyybzZXk+qgD0ErxdUL7/x1nn4EHc=; b=jGmRKaHjiB0LJjuSUiCQxNuc0IQU6ggQnRYlQc5lU2gNvcToeTo/ZDpq3fDTJFmiy61YsT fd/IuOQXQx5ZTYzw/1yiGDfqlhwZcClL4HqECu10DBBA/ljjUOk8Wk0ByScFt0RA5WFzBy EBlts6L764k93fDF645Tw7QRW/j4dFk= Received: from suse.cz (unknown [10.100.201.86]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id E91A4A3B95; Tue, 31 Aug 2021 09:59:08 +0000 (UTC) Date: Tue, 31 Aug 2021 11:59:05 +0200 From: Michal Hocko To: Johannes Weiner Cc: Rik van Riel , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, stable@kernel.org, Chris Down 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 Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 5E7701903 Authentication-Results: imf22.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=jGmRKaHj; dmarc=pass (policy=quarantine) header.from=suse.com; spf=pass (imf22.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.28 as permitted sender) smtp.mailfrom=mhocko@suse.com X-Rspamd-Server: rspam01 X-Stat-Signature: kgd8gr8wzdh68iaq186ejewfyi5jdqat X-HE-Tag: 1630403951-475964 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon 30-08-21 16:48:03, Johannes Weiner wrote: > On Thu, Aug 26, 2021 at 10:01:49PM -0400, Rik van Riel wrote: [...] > > 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); > > I have no overly strong preferences, but if Michal prefers max(), how about: > > cgroup_size = max3(cgroup_size, protection, 1); Yes this is better. > Or go back to not taking the branch in the first place when there is > no protection in effect... > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 6247f6f4469a..9c200bb3ae51 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -2547,7 +2547,7 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc, > mem_cgroup_protection(sc->target_mem_cgroup, memcg, > &min, &low); > > - if (min || low) { > + if (min || (!sc->memcg_low_reclaim && low)) { > /* > * Scale a cgroup's reclaim pressure by proportioning > * its current usage to its memory.low or memory.min This is slightly more complex to read but it is also better than +1 trick. Either of the two work for me. -- Michal Hocko SUSE Labs