Messages in this thread | | | From | David Hildenbrand <> | Subject | Re: [PATCH] mm: be more verbose for alloc_contig_range faliures | Date | Thu, 18 Feb 2021 17:26:08 +0100 |
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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.
> 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.
-- Thanks,
David / dhildenb
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