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 1A22DC433E0 for ; Thu, 18 Feb 2021 18:53:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C622F61606 for ; Thu, 18 Feb 2021 18:53:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233486AbhBRSw7 (ORCPT ); Thu, 18 Feb 2021 13:52:59 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:29028 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234036AbhBRQzU (ORCPT ); Thu, 18 Feb 2021 11:55:20 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1613667208; 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=YtvcWwzeSACTJqsYxD6kx8htzZr8ZHgABHYpks1GT1A=; b=ZKPmO0JBqNaOTm94M8vxAf2P2kes4EooGbl1K8tNt9KotJ1Ba0YGasgPiidx6v9ID7/64G HmDXBo0AXchdrJvRTxiVHqKA8IcCG5XgZj+Bb3d+GEnd1vSU3K0hxVsnLSfGxx+GSuoKHq Cx3hWzROZe6nLvSRjV/+CaaeuvzxYNw= 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-263-tyElYNPvMQ23DwZnrgx_1Q-1; Thu, 18 Feb 2021 11:53:26 -0500 X-MC-Unique: tyElYNPvMQ23DwZnrgx_1Q-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 86034107ACC7; Thu, 18 Feb 2021 16:53:25 +0000 (UTC) Received: from [10.36.114.59] (ovpn-114-59.ams2.redhat.com [10.36.114.59]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0C65B5D9C6; Thu, 18 Feb 2021 16:53:23 +0000 (UTC) Subject: Re: [PATCH] mm: be more verbose for alloc_contig_range faliures To: Minchan Kim Cc: Michal Hocko , 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: <694c1d6a-d3bc-71ec-7730-e83714e85c25@redhat.com> Date: Thu, 18 Feb 2021 17:53:22 +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 10.5.11.14 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 18.02.21 17:47, Minchan Kim wrote: > On Thu, Feb 18, 2021 at 05:26:08PM +0100, David Hildenbrand wrote: >> On 18.02.21 17:19, 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. >> >> I am not 100% sure it does. > > Oh, it should. Otherwise, let's fix either of caller or > alloc_contig_range since we have a customer. > > ``` > ret = alloc_contig_range(pfn, pfn + count, MIGRATE_CMA, > GFP_KERNEL | (no_warn ? __GFP_NOWARN : 0)) > ``` > Oh, interesting. So I certainly want to add that for virtio-mem as well - thanks. And discussed, we should hide the one pr_info... in alloc_contig_range() as well. >> >>> Why shouldn't people use it if they don't care the failure? >> >> Because flooding the log with noise maybe a handful of people on this planet >> care about is absolutely useless. With the warnings in warn_alloc() people >> can at least conclude something reasonable. >> >>> Semantically, it makes sense to me. >>> >>> About the messeage flooding, shouldn't we go with ratelimiting? >> >> At least that (see warn_alloc()). But I'd even want to see some other >> trigger to enable this explicitly on demand. > > No objection. > > How about adding verbose knob under CONFIG_CMA_DEBUGFS with > alloc_contig_range(..., bool verbose) like start_isolate_page_range? > > If admin turns on the verbose mode under CONFIG_CMA_DEBUGFS, > cma_alloc will pass alloc_contig_range(...., true). I'd handle this internally in alloc_contig_range and not pass magic flags around. Some kind of debug knob to enable advanced messages (exceeding the usual allocation warnings we would usually see). -- Thanks, David / dhildenb