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

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Message-ID: <YC402s1vqvC4q041@dhcp22.suse.cz>
Date:   Thu, 18 Feb 2021 10:35:22 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     David Hildenbrand <david@...hat.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 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.
-- 
Michal Hocko
SUSE Labs