From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f199.google.com (mail-io0-f199.google.com [209.85.223.199]) by kanga.kvack.org (Postfix) with ESMTP id 10F896B02F7 for ; Tue, 28 Nov 2017 06:05:56 -0500 (EST) Received: by mail-io0-f199.google.com with SMTP id h205so345745iof.15 for ; Tue, 28 Nov 2017 03:05:56 -0800 (PST) Received: from mail-sor-f41.google.com (mail-sor-f41.google.com. [209.85.220.41]) by mx.google.com with SMTPS id f84sor14006434ioi.360.2017.11.28.03.05.55 for (Google Transport Security); Tue, 28 Nov 2017 03:05:55 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20171128104810.5f3lvby64i6x54id@dhcp22.suse.cz> References: <1506592464-30962-1-git-send-email-laoar.shao@gmail.com> <20171127091939.tahb77nznytcxw55@dhcp22.suse.cz> <20171128103723.GK5977@quack2.suse.cz> <20171128104810.5f3lvby64i6x54id@dhcp22.suse.cz> From: Yafang Shao Date: Tue, 28 Nov 2017 19:05:54 +0800 Message-ID: Subject: Re: [PATCH] Revert "mm/page-writeback.c: print a warning if the vm dirtiness settings are illogical" (was: Re: [PATCH] mm: print a warning once the vm dirtiness settings is illogical) Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Jan Kara , Tetsuo Handa , Andrew Morton , Linux MM 2017-11-28 18:48 GMT+08:00 Michal Hocko : > On Tue 28-11-17 11:37:23, Jan Kara wrote: >> On Mon 27-11-17 10:19:39, Michal Hocko wrote: >> > Andrew, >> > could you simply send this to Linus. If we _really_ need something to >> > prevent misconfiguration, which I doubt to be honest, then it should be >> > thought through much better. >> >> What's so bad about the warning? I think warning about such >> misconfiguration is not a bad thing per se. Maybe it should be ratelimited >> and certainly the condition is too loose as your example shows but in >> principle I'm not against it and e.g. making the inequality in the condition >> strict like: >> >> if (unlikely(bg_thresh > thresh)) >> >> or at least >> >> if (unlikely(bg_thresh >= thresh && thresh > 0)) >> >> would warn about cases where domain_dirty_limits() had to fixup bg_thresh >> manually to make writeback throttling work and avoid reclaim stalls which >> is IMHO a sane thing... > > If it generates false positives then it is more harmful than useful. And > even if it doesn't, what is the point? Do we check that other related > knobs are configured properly? I do not think so, we simply rely on > admins doing sane things. Not all admins are good at tuning this. I don't think every SE knows how to tune vm.dirty_background_bytes and vm.dirty_background_bytes. Only kernel experts could do that. At least this warning could help them to learn what happend instead of knowing nothing. > Otherwise we would have a lot of warnings like > that. They would be pain to maintain and I believe the additional value > is quite dubious. > -- -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org