From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk0-f200.google.com (mail-qk0-f200.google.com [209.85.220.200]) by kanga.kvack.org (Postfix) with ESMTP id 35A206B0038 for ; Sat, 22 Apr 2017 04:17:51 -0400 (EDT) Received: by mail-qk0-f200.google.com with SMTP id x128so10953235qkb.14 for ; Sat, 22 Apr 2017 01:17:51 -0700 (PDT) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id z94si12300718qtd.139.2017.04.22.01.17.49 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 22 Apr 2017 01:17:50 -0700 (PDT) Date: Sat, 22 Apr 2017 10:10:34 +0200 From: Stanislaw Gruszka Subject: Re: [PATCH] mm,page_alloc: Split stall warning and failure warning. Message-ID: <20170422081030.GA5476@redhat.com> References: <1491825493-8859-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> <20170410150308.c6e1a0213c32e6d587b33816@linux-foundation.org> <201704182049.BIE34837.FJOFOMFOQSLHVt@I-love.SAKURA.ne.jp> <20170419111342.GF29789@dhcp22.suse.cz> <20170419132212.GA3514@redhat.com> <20170419133339.GI29789@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170419133339.GI29789@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: David Rientjes , Tetsuo Handa , akpm@linux-foundation.org, linux-mm@kvack.org, hannes@cmpxchg.org On Wed, Apr 19, 2017 at 03:33:39PM +0200, Michal Hocko wrote: > On Wed 19-04-17 15:22:16, Stanislaw Gruszka wrote: > > On Wed, Apr 19, 2017 at 01:13:43PM +0200, Michal Hocko wrote: > > > On Tue 18-04-17 14:47:32, David Rientjes wrote: > > > [...] > > > > I think the debug_guardpage_minorder() check makes sense for failed > > > > allocations because we are essentially removing memory from the system for > > > > debug, failed allocations as a result of low on memory or fragmentation > > > > aren't concerning if we are removing memory from the system. > > > > > > I really fail to see how this is any different from booting with > > > mem=$SIZE to reduce the amount of available memory. > > > > mem= shrink upper memory limit, debug_guardpage_minorder= fragments > > available physical memory (deliberately to catch unintended access). > > Yeah but both make allocation failures (especially higher order ones) > more likely. So I really fail to see the point inhibit allocation > failure warning for one and not for the other. There is difference for buddy allocator. If you limit to 1/2 of memory such only upper half is not available, buddy allocator can easily find pages for higher order allocations in lower half of memory. When you limit to 1/2 of memory such every second page is not available, buddy allocator can not make successful any order 1 or higher allocations. > This whole special casing > of debug_guardpage_minorder is just too strange to me. We do have a rate > limit to not flood the log. I added this check to skip warning if buddy allocator fail, what I considered likely scenario taking the conditions. The check remove warning completely, rate limit only limit the speed warnings shows in logs. Stanislaw -- 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