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 68C3E6B0033 for ; Sun, 26 Nov 2017 03:27:04 -0500 (EST) Received: by mail-io0-f198.google.com with SMTP id a72so17577454ioe.13 for ; Sun, 26 Nov 2017 00:27:04 -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 j30sor8610653ioo.196.2017.11.26.00.27.03 for (Google Transport Security); Sun, 26 Nov 2017 00:27:03 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <201711261703.HDI52138.JSFVOFOtHLMOFQ@I-love.SAKURA.ne.jp> References: <1506592464-30962-1-git-send-email-laoar.shao@gmail.com> <201711261142.EIE82842.LFOtSHOFVOFJQM@I-love.SAKURA.ne.jp> <201711261703.HDI52138.JSFVOFOtHLMOFQ@I-love.SAKURA.ne.jp> From: Yafang Shao Date: Sun, 26 Nov 2017 16:27:02 +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: Tetsuo Handa Cc: Andrew Morton , Jan Kara , Michal Hocko , Linux MM 2017-11-26 16:03 GMT+08:00 Tetsuo Handa : > Yafang Shao wrote: >> >> I have also verified your test code on my machine, but can not find >> >> this message. >> >> >> > >> > Not always printed. It is timing dependent. >> > >> >> I will try and analysis why this happen. >> > I see. > > Here is dump of variables. Always mostly 0 when this happens. > > --- a/mm/page-writeback.c > +++ b/mm/page-writeback.c > @@ -434,7 +434,8 @@ static void domain_dirty_limits(struct dirty_throttle_control *dtc) > bg_thresh = (bg_ratio * available_memory) / PAGE_SIZE; > > if (unlikely(bg_thresh >= thresh)) { > - pr_warn("vm direct limit must be set greater than background limit.\n"); > + pr_warn("vm direct limit must be set greater than background limit. bg_thresh=%lu thresh=%lu bg_bytes=%lu bytes=%lu bg_ratio=%lu ratio=%lu gdtc=%p gdtc->vail=%lu vm_dirty_bytes=%lu dirty_background_bytes=%lu\n", > + bg_thresh, thresh, bg_bytes, bytes, bg_ratio, ratio, gdtc, gdtc ? gdtc->avail : 0UL, vm_dirty_bytes, dirty_background_bytes); > bg_thresh = thresh / 2; > } > > [ 259.641324] vm direct limit must be set greater than background limit. bg_thresh=0 thresh=0 bg_bytes=0 bytes=0 bg_ratio=409 ratio=1228 gdtc= (null) gdtc->vail=0 vm_dirty_bytes=0 dirty_background_bytes=0 > [ 317.798913] vm direct limit must be set greater than background limit. bg_thresh=0 thresh=0 bg_bytes=0 bytes=0 bg_ratio=409 ratio=1228 gdtc= (null) gdtc->vail=0 vm_dirty_bytes=0 dirty_background_bytes=0 > [ 317.798935] vm direct limit must be set greater than background limit. bg_thresh=0 thresh=0 bg_bytes=0 bytes=0 bg_ratio=409 ratio=1228 gdtc= (null) gdtc->vail=0 vm_dirty_bytes=0 dirty_background_bytes=0 > [ 317.976210] vm direct limit must be set greater than background limit. bg_thresh=0 thresh=0 bg_bytes=0 bytes=0 bg_ratio=409 ratio=1228 gdtc= (null) gdtc->vail=0 vm_dirty_bytes=0 dirty_background_bytes=0 > [ 417.781194] vm direct limit must be set greater than background limit. bg_thresh=0 thresh=0 bg_bytes=0 bytes=0 bg_ratio=409 ratio=1228 gdtc= (null) gdtc->vail=0 vm_dirty_bytes=0 dirty_background_bytes=0 > [ 466.322615] vm direct limit must be set greater than background limit. bg_thresh=0 thresh=0 bg_bytes=0 bytes=0 bg_ratio=409 ratio=1228 gdtc= (null) gdtc->vail=0 vm_dirty_bytes=0 dirty_background_bytes=0 > [ 466.322618] vm direct limit must be set greater than background limit. bg_thresh=0 thresh=0 bg_bytes=0 bytes=0 bg_ratio=409 ratio=1228 gdtc= (null) gdtc->vail=0 vm_dirty_bytes=0 dirty_background_bytes=0 > [ 466.497893] vm direct limit must be set greater than background limit. bg_thresh=0 thresh=0 bg_bytes=0 bytes=0 bg_ratio=409 ratio=1228 gdtc= (null) gdtc->vail=0 vm_dirty_bytes=0 dirty_background_bytes=0 > [ 466.504687] vm direct limit must be set greater than background limit. bg_thresh=0 thresh=0 bg_bytes=0 bytes=0 bg_ratio=409 ratio=1228 gdtc= (null) gdtc->vail=0 vm_dirty_bytes=0 dirty_background_bytes=0 Hi Tetsuo, Bellow is the code analysis, // global_dirtyable_memory() will return number of globally dirtyable page gdtc.avail = global_dirtyable_memory(); domain_dirty_limits(&gdtc); unsigned long ratio = (vm_dirty_ratio * PAGE_SIZE) / 100; // 1228 unsigned long bg_ratio = (dirty_background_ratio * PAGE_SIZE) / 100; // 409 available_memory = dtc->avail; thresh = (ratio * available_memory) / PAGE_SIZE; bg_thresh = (bg_ratio * available_memory) / PAGE_SIZE; So if available_memory is less than 4 pages, thresh and bg_thresh will be both 0, then the message will be printed. 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