From: Michal Hocko <mhocko@suse.com>
To: David Hildenbrand <david@redhat.com>
Cc: Minchan Kim <minchan@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
joaodias@google.com
Subject: Re: [PATCH] mm: be more verbose for alloc_contig_range faliures
Date: Fri, 19 Feb 2021 11:02:13 +0100 [thread overview]
Message-ID: <YC+MpecknddNQ4+o@dhcp22.suse.cz> (raw)
In-Reply-To: <45f1bffe-8a0b-2969-32d4-e24a911a647d@redhat.com>
On Fri 19-02-21 10:30:12, David Hildenbrand wrote:
> On 19.02.21 10:28, 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.
> >
> > 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.
> >
> > 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.
> >
> > 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
> > infrastructure for this.
>
> Just so I understand what you are referring to - trace points?
Documentation/admin-guide/dynamic-debug-howto.rst
but I have to confess I have 0 experience with this.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2021-02-19 10:02 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-17 16:36 [PATCH] mm: be more verbose for alloc_contig_range faliures Minchan Kim
2021-02-17 16:51 ` David Hildenbrand
2021-02-17 17:26 ` Minchan Kim
2021-02-17 17:34 ` David Hildenbrand
2021-02-17 17:45 ` Minchan Kim
2021-02-18 8:56 ` Michal Hocko
2021-02-18 9:02 ` David Hildenbrand
2021-02-18 9:35 ` Michal Hocko
2021-02-18 9:43 ` David Hildenbrand
2021-02-18 9:59 ` Michal Hocko
2021-02-18 16:19 ` Minchan Kim
2021-02-18 16:26 ` David Hildenbrand
2021-02-18 16:47 ` Minchan Kim
2021-02-18 16:53 ` David Hildenbrand
2021-02-19 9:28 ` Michal Hocko
2021-02-19 9:30 ` David Hildenbrand
2021-02-19 10:02 ` Michal Hocko [this message]
2021-02-19 10:34 ` David Hildenbrand
[not found] ` <YD50pcPuwV456vwm@google.com>
2021-03-04 16:01 ` Minchan Kim
2021-03-04 16:10 ` David Hildenbrand
2021-03-04 16:23 ` Minchan Kim
2021-03-04 16:28 ` David Hildenbrand
2021-03-04 17:11 ` Minchan Kim
2021-03-04 17:23 ` David Hildenbrand
2021-03-04 18:11 ` Minchan Kim
2021-03-04 18:22 ` Minchan Kim
2021-03-08 12:49 ` Michal Hocko
2021-03-08 13:22 ` David Hildenbrand
2021-03-08 14:11 ` Michal Hocko
2021-03-08 14:13 ` David Hildenbrand
2021-03-08 15:42 ` Michal Hocko
2021-03-08 15:58 ` Minchan Kim
2021-03-08 16:21 ` Michal Hocko
2021-03-08 17:01 ` Minchan Kim
2021-03-08 20:27 ` Minchan Kim
2021-02-18 16:10 ` Minchan Kim
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