From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f198.google.com (mail-io0-f198.google.com [209.85.223.198]) by kanga.kvack.org (Postfix) with ESMTP id 023D26B0253 for ; Mon, 27 Nov 2017 03:29:15 -0500 (EST) Received: by mail-io0-f198.google.com with SMTP id g73so35238122ioj.0 for ; Mon, 27 Nov 2017 00:29:14 -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 200sor4746609itf.108.2017.11.27.00.29.14 for (Google Transport Security); Mon, 27 Nov 2017 00:29:14 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20171127082112.b7elnzy24qiqze46@dhcp22.suse.cz> References: <201711261142.EIE82842.LFOtSHOFVOFJQM@I-love.SAKURA.ne.jp> <201711261703.HDI52138.JSFVOFOtHLMOFQ@I-love.SAKURA.ne.jp> <201711261938.BCD34864.QLVFOSJFHOtOFM@I-love.SAKURA.ne.jp> <20171127082112.b7elnzy24qiqze46@dhcp22.suse.cz> From: Yafang Shao Date: Mon, 27 Nov 2017 16:29:13 +0800 Message-ID: Subject: 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: Tetsuo Handa , Andrew Morton , Jan Kara , Linux MM , fcicq@fcicq.net 2017-11-27 16:21 GMT+08:00 Michal Hocko : > On Mon 27-11-17 16:06:50, Yafang Shao wrote: >> +cc fcicq > [...] >> diff --git a/mm/page-writeback.c b/mm/page-writeback.c >> index 8a15511..6c5c018 100644 >> --- a/mm/page-writeback.c >> +++ b/mm/page-writeback.c >> @@ -377,7 +377,16 @@ static unsigned long global_dirtyable_memory(void) >> if (!vm_highmem_is_dirtyable) >> x -= highmem_dirtyable_memory(x); >> >> - return x + 1; /* Ensure that we never return 0 */ >> + /* >> + * - Why 100 ? >> + * - Because the return value will be used by dirty ratio and >> + * dirty background ratio to calculate dirty thresh and bg thresh, >> + * so if the return value is two small, the thresh value maybe >> + * calculated to 0. >> + * As the max value of ratio is 100, so the return value is added >> + * by 100 here. >> + */ >> + return x + 100; > > No. We should just revert 0f6d24f87856 ("mm/page-writeback.c: print a > warning if the vm dirtiness settings are illogical") because it is of a > dubious value and it causes problems. I am not even sure why it got > merged. It doesn't have any ack or review and I remember objecting to > the patch previously as pointless. > -- It is reviewed and merged by Andrew. >>From Andrew: > I think this means that a script which alters both dirty_bytes and dirty_background_bytes must alter dirty_background_bytes first if they are being decreased and must alter dirty_bytes first if they are being increased. Or something like that. It will help us to find the error if we don't change these values like this. Thanks Yafang -- 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