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Thu, 18 Feb 2021 08:19:53 -0800 (PST) Received: from google.com ([2620:15c:211:201:157d:8a19:5427:ea9e]) by smtp.gmail.com with ESMTPSA id q15sm5979199pja.22.2021.02.18.08.19.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 18 Feb 2021 08:19:52 -0800 (PST) Date: Thu, 18 Feb 2021 08:19:50 -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: 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 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. About the messeage flooding, shouldn't we go with ratelimiting? I see those two problem are orthgonal.