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=-4.0 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,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 478ECC1550B for ; Thu, 4 Mar 2021 16:25:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2A60064F4D for ; Thu, 4 Mar 2021 16:25:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237506AbhCDQYj (ORCPT ); Thu, 4 Mar 2021 11:24:39 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59060 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237042AbhCDQYL (ORCPT ); Thu, 4 Mar 2021 11:24:11 -0500 Received: from mail-pf1-x431.google.com (mail-pf1-x431.google.com [IPv6:2607:f8b0:4864:20::431]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E7829C061574 for ; Thu, 4 Mar 2021 08:23:30 -0800 (PST) Received: by mail-pf1-x431.google.com with SMTP id q204so18239785pfq.10 for ; Thu, 04 Mar 2021 08:23:30 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=TnV5xh27yXeZ4eD0NfKduGmV3dmdCvMkiedYReyJGMA=; b=BPlF8iIERigTBaVyE76361mJ2TFY40HPNF1YC/AYP64fCsRzFPYiN5tFdwOf90a+QG erbUI9t9cLfeCBAUqByVfGhhQP9IftqW66Sv8Q4bJ7hTtHGr7ReXC2FNm35yHNnspP9+ aXRuA0hSbRQJbXWKNAM/7eNKVp77csBgWgB94oHbHwkApiay4GlXiXbnLgxMIuiJlm8e 0V5hqkUvhRIOR7bgijnmydI4PENNsdCQmYEu7RSBDe6JR3ZrcB83urJkq8XtwCgXN4pI /5n2/+/Z9p/foHgCRe1Fs+8eq/guwm+vNrmSETsFmjjdBZHTQnmKUFVrpWybfHkb6HHL FRJw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to; bh=TnV5xh27yXeZ4eD0NfKduGmV3dmdCvMkiedYReyJGMA=; b=rR7VyFIzKeQy/9O8G8aTE0+eHo+ktZjDl95xZvBR6VRLRhYcNArJBqRRQ1f0Vj9JZU MRU/fSnEbafVOiYoemIh5vtaz5QMFKjjSXQ33PIjSkkmSHv3v7c79OeCz99xKLhP4aaw PPqzHytVdQznoT703GkJQEZb0OnNClmM46UbGTbsFhr4vhzMyvFiT71onwhsD1h2jgN7 LEGS5n+6IwCr1NEPFjEyg78oHTGw4CZN3f7ACh+OUWBdde2CYMqQ2NpVNWKnLdeWyZLV u3Xy81afNpaO/t6lZ2GCkzO5rN1WCmKE50qSrli12PRelVBRJEdQPFxBw2uBL+SJfCHT 10TA== X-Gm-Message-State: AOAM533tLPYbLDEAcZ8cMaI7CccZeyQXBYrypCF5fRWCSzl4KlzQatBI v00+075EofHm35FjNMWSHYsBQ2I6AHI= X-Google-Smtp-Source: ABdhPJyzhgLCrmXNVbPtrQKAC+jWQrzbWipOAiofwKzxYQvN2olIHaz/xXVbKE8ojz/EfRKAbFCYIA== X-Received: by 2002:a62:7a52:0:b029:1ee:ee21:50f with SMTP id v79-20020a627a520000b02901eeee21050fmr4357651pfc.14.1614875010402; Thu, 04 Mar 2021 08:23:30 -0800 (PST) Received: from google.com ([2620:15c:211:201:edb1:8010:5c27:a8cc]) by smtp.gmail.com with ESMTPSA id il6sm7894107pjb.56.2021.03.04.08.23.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 04 Mar 2021 08:23:29 -0800 (PST) Sender: Minchan Kim Date: Thu, 4 Mar 2021 08:23:27 -0800 From: Minchan Kim To: David Hildenbrand Cc: Michal Hocko , 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 04, 2021 at 05:10:52PM +0100, David Hildenbrand wrote: > On 04.03.21 17:01, Minchan Kim wrote: > > On Tue, Mar 02, 2021 at 09:23:49AM -0800, Minchan Kim wrote: > > > On Fri, Feb 19, 2021 at 10:28:12AM +0100, 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. > > > > > > Sorry for the late response. > > > > > > > > > > > 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. > > > > > > That was why I'd like to approach for per-call site indicator with > > > __GFP_NOWARN. Even though it was allocation from CMA, some of them > > > wouldn't be critical for the failure so those wouldn't care of > > > the failure. cma_alloc already has carried on "bool no_warn" > > > which was changed into gfp_t recently. What alloc_contig_range > > > should do is to take care of the request. > > > > > > > > > > > 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. > > > > > > Totally, agree dumping thounds of pages as debugging aid are bad. > > > Couldn't we simply ratelimit them like other places? > > > > > > > > > > > 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 > > > > > > I agree the rest of the places are GFP_NOWARN by default except CMA > > > if they expect alloc_contig_range are optimistic allocation request. > > > However, I'd like to tweak it for CMA - accept gfp_t from cma_alloc > > > and take care of the __GFP_NOWARN since some sites of CMA could be > > > fault tolerant so no need to get the warning. > > > > Any thought to proceed? > > IMHO, add some proper debug mechanisms and don't try squeezing debug > messages into "WARN" semantics. > > Any alloc_contig_range() user can benefit from that. So the point is how we could add proper debug mechanism here. Think about call site A is not critical for the failure but called very frquently. Call site B is critical for the failure but called very rarely so turns on system wide dynamic debugging. You could see a lot of debug message from A even though we dont't want it. Even, it could hide B's debugging message by ratelimiting.