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

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Message-ID: <YEZF81vXGR8TX8sE@dhcp22.suse.cz>
Date:   Mon, 8 Mar 2021 16:42:43 +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 Mon 08-03-21 15:13:35, David Hildenbrand wrote:
> On 08.03.21 15:11, Michal Hocko wrote:
> > On Mon 08-03-21 14:22:12, David Hildenbrand wrote:
> > > On 08.03.21 13:49, Michal Hocko wrote:
> > [...]
> > > > Earlier in the discussion I have suggested dynamic debugging facility.
> > > > Documentation/admin-guide/dynamic-debug-howto.rst. Have you tried to
> > > > look into that direction?
> > > 
> > > Did you see the previous mail this is based on:
> > > 
> > > https://lkml.kernel.org/r/YEEUq8ZRn4WyYWVx@google.com
> > > 
> > > I agree that "nofail" is misleading. Rather something like
> > > "dump_on_failure", just a better name :)
> > 
> > Yeah, I have read through the email thread. I just do not get why we
> > cannot make it pr_debug() and add -DDYNAMIC_DEBUG_MODULE for
> > page_alloc.c (I haven't checked whether that is possible for built in
> > compile units, maybe it is not but from a quick seems it should).
> > 
> > I really do not like this to be a part of the API. alloc_contig_range is
> 
> Which API?

Any level of the alloc_contig_range api because I strongly suspect that
once there is something on the lower levels there will be a push to have
it in the directly consumed api as well. Besides that I think this is
just a wrong way to approach the problem.

> It does not affect alloc_contig_range() itself, it's used
> internally only. Sure, we could simply pr_debug() for each and every
> migration failure. As long as it's default-disabled, sure.
> 
> I do agree that we should look into properly including this into the dynamic
> debugging ifrastructure.

Yeah, unless we learn this is not feasible for some reason, which I do
not see right now, then let's just make it pr_debug with the runtime
control.
-- 
Michal Hocko
SUSE Labs