linux-kernel - Re: [PATCH] mm: be more verbose for alloc_contig

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Message-ID: <fa8195f9-4d1b-7a77-1a02-d69710f4208b@redhat.com>
Date:   Thu, 18 Feb 2021 10:43:21 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>, joaodias@...gle.com
Subject: Re: [PATCH] mm: be more verbose for alloc_contig_range faliures

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.

-- 
Thanks,

David / dhildenb