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Thu, 04 Mar 2021 08:01:17 -0800 (PST) Received: from google.com ([2620:15c:211:201:edb1:8010:5c27:a8cc]) by smtp.gmail.com with ESMTPSA id q4sm27838853pfs.134.2021.03.04.08.01.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 04 Mar 2021 08:01:16 -0800 (PST) Date: Thu, 4 Mar 2021 08:01:15 -0800 From: Minchan Kim To: Michal Hocko Cc: David Hildenbrand , 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: X-Stat-Signature: s1ssp7mrsuwksia9ijq8mqf9sza6jcpg X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 1672420053CE Received-SPF: none (gmail.com>: No applicable sender policy available) receiver=imf28; identity=mailfrom; envelope-from=""; helo=mail-pf1-f171.google.com; client-ip=209.85.210.171 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1614873679-619501 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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? > > > infrastructure for this. > > dynamic debugging is system wide flag so how to deal with if we > want to see specific alloation faliure, not whole callsites? > That's why I'd like to go with per-call site approach, still.