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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 538A2C433DB for ; Fri, 19 Feb 2021 10:03:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0E98D64E92 for ; Fri, 19 Feb 2021 10:03:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230222AbhBSKDF (ORCPT ); Fri, 19 Feb 2021 05:03:05 -0500 Received: from mx2.suse.de ([195.135.220.15]:56616 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229726AbhBSKDB (ORCPT ); Fri, 19 Feb 2021 05:03:01 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1613728934; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=9Z3FMU+NZ9Au0nCTE6kg8lS5ts8nrWXs/miKjuzDFtY=; b=YmENC6JsX2Xin2amX6vYdQ1eR3UUB2l++vL+t7eJMpi60Lr6/PtR3PO3l9g7Y4DLJLYP7D Y+AjBlgZeNpOnhChCOXGbcp8PKVaYj58K4+VpHNkPkE52Qmngzwf5ziHDAESewvePskmzL 4djNQCHNjUjx9ljdU94aodvIlsLmxOM= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 9D807ACBF; Fri, 19 Feb 2021 10:02:14 +0000 (UTC) Date: Fri, 19 Feb 2021 11:02:13 +0100 From: Michal Hocko To: David Hildenbrand Cc: Minchan Kim , Andrew Morton , linux-mm , LKML , joaodias@google.com Subject: Re: [PATCH] mm: be more verbose for alloc_contig_range faliures Message-ID: References: <20210217163603.429062-1-minchan@kernel.org> <2f167b3c-5f0a-444a-c627-49181fc8fe0d@redhat.com> <45f1bffe-8a0b-2969-32d4-e24a911a647d@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <45f1bffe-8a0b-2969-32d4-e24a911a647d@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 19-02-21 10:30:12, David Hildenbrand wrote: > 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? Documentation/admin-guide/dynamic-debug-howto.rst but I have to confess I have 0 experience with this. -- Michal Hocko SUSE Labs