linux-kernel - Re: [patch -mm] mm, page_alloc: warn_alloc nodemask is NULL when cpusets are disabled

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Date:   Thu, 19 Jan 2017 09:57:07 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     David Rientjes <rientjes@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [patch -mm] mm, page_alloc: warn_alloc nodemask is NULL when
 cpusets are disabled

On Thu 19-01-17 08:29:45, Vlastimil Babka wrote:
> On 01/18/2017 10:51 PM, David Rientjes wrote:
> > The patch "mm, page_alloc: warn_alloc print nodemask" implicitly sets the 
> > allocation nodemask to cpuset_current_mems_allowed when there is no 
> > effective mempolicy.  cpuset_current_mems_allowed is only effective when 
> > cpusets are enabled, which is also printed by warn_alloc(), so setting 
> > the nodemask to cpuset_current_mems_allowed is redundant and prevents 
> > debugging issues where ac->nodemask is not set properly in the page 
> > allocator.
> > 
> > This provides better debugging output since 
> > cpuset_print_current_mems_allowed() is already provided.
> > 
> > Signed-off-by: David Rientjes <rientjes@...gle.com>
> 
> Yes, with my current cpuset vs mempolicy debugging experience, this is
> more useful (except how both nodemask and mems_allowed can change under
> us, so what we print here is not necessarily the same that what
> get_page_from_freelist() has seen, but that's another thing...).
> 
> But I would suggest you change the oom killer's dump_header() the same
> way than warn_alloc().

Yes please

-- 
Michal Hocko
SUSE Labs