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=-7.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 8A597C433DB for ; Fri, 19 Feb 2021 09:31:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2879064ED5 for ; Fri, 19 Feb 2021 09:31:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230079AbhBSJbt (ORCPT ); Fri, 19 Feb 2021 04:31:49 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:59740 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229927AbhBSJbq (ORCPT ); Fri, 19 Feb 2021 04:31:46 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1613727020; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=q3JTcUNa5wlSteHsee83SOzVlisb9YCuNoGlOsx95po=; b=W3SGjBOUJstfR5ULx3yz8iVAPg7ZPB21kJ2I6jL25nqvaEZeXbbwuatk2pMfvjjiXYPZg8 ICmf2w2PIpaEipNn2fmgqVV/jVazD8gN40z4EXfYdAq1w22tT36CFvY4VOsse/1IDYNAU4 dmxN7Y6k+u+j+43h9oqJajD+k35kKhw= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-376-wkwvDw66MRCzjmK3m0DxnA-1; Fri, 19 Feb 2021 04:30:16 -0500 X-MC-Unique: wkwvDw66MRCzjmK3m0DxnA-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id AA4EC1020C39; Fri, 19 Feb 2021 09:30:14 +0000 (UTC) Received: from [10.36.113.117] (ovpn-113-117.ams2.redhat.com [10.36.113.117]) by smtp.corp.redhat.com (Postfix) with ESMTP id 551E6171FE; Fri, 19 Feb 2021 09:30:13 +0000 (UTC) Subject: Re: [PATCH] mm: be more verbose for alloc_contig_range faliures To: Michal Hocko , Minchan Kim Cc: Andrew Morton , linux-mm , LKML , joaodias@google.com References: <20210217163603.429062-1-minchan@kernel.org> <2f167b3c-5f0a-444a-c627-49181fc8fe0d@redhat.com> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: <45f1bffe-8a0b-2969-32d4-e24a911a647d@redhat.com> Date: Fri, 19 Feb 2021 10:30:12 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19.02.21 10:28, Michal Hocko wrote: > On Thu 18-02-21 08:19:50, Minchan Kim wrote: >> On Thu, Feb 18, 2021 at 10:43:21AM +0100, David Hildenbrand wrote: >>> On 18.02.21 10:35, Michal Hocko wrote: >>>> On Thu 18-02-21 10:02:43, David Hildenbrand wrote: >>>>> On 18.02.21 09:56, Michal Hocko wrote: >>>>>> On Wed 17-02-21 08:36:03, Minchan Kim wrote: >>>>>>> alloc_contig_range is usually used on cma area or movable zone. >>>>>>> It's critical if the page migration fails on those areas so >>>>>>> dump more debugging message like memory_hotplug unless user >>>>>>> specifiy __GFP_NOWARN. >>>>>> >>>>>> I agree with David that this has a potential to generate a lot of output >>>>>> and it is not really clear whether it is worth it. Page isolation code >>>>>> already has REPORT_FAILURE mode which currently used only for the memory >>>>>> hotplug because this was just too noisy from the CMA path - d381c54760dc >>>>>> ("mm: only report isolation failures when offlining memory"). >>>>>> >>>>>> Maybe migration failures are less likely to fail but still. >>>>> >>>>> Side note: I really dislike that uncontrolled error reporting on memory >>>>> offlining path we have enabled as default. Yeah, it might be useful for >>>>> ZONE_MOVABLE in some cases, but otherwise it's just noise. >>>>> >>>>> Just do a "sudo stress-ng --memhotplug 1" and see the log getting flooded >>>> >>>> Anyway we can discuss this in a separate thread but I think this is not >>>> a representative workload. >>> >>> Sure, but the essence is "this is noise", and we'll have more noise on >>> alloc_contig_range() as we see these calls more frequently. There should be >>> an explicit way to enable such *debug* messages. >> >> alloc_contig_range already has gfp_mask and it respects __GFP_NOWARN. >> Why shouldn't people use it if they don't care the failure? >> Semantically, it makes sense to me. > > Well, alloc_contig_range doesn't really have to implement all the gfp > flags. This is a matter of practicality. alloc_contig_range is quite > different from the page allocator because it is to be expected that it > can fail the request. This is avery optimistic allocation request. That > would suggest that complaining about allocation failures is rather > noisy. > > Now I do understand that some users would like to see why those > allocations have failed. The question is whether that information is > generally useful or it is more of a debugging aid. The amount of > information is also an important aspect. It would be rather unfortunate > to dump thousands of pages just because they cannot be migrated. > > I do not have a strong opinion here. We can make all alloc_contig_range > users use GFP_NOWARN by default and only skip the flag from the cma > allocator but I am slowly leaning towards (ab)using dynamic debugging > infrastructure for this. Just so I understand what you are referring to - trace points? -- Thanks, David / dhildenb