linux-kernel - Re: [patch 2/3] mm, oom: remove unnecessary check for NULL zonelist

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Date:	Fri, 1 Aug 2014 14:42:19 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>
cc:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [patch 2/3] mm, oom: remove unnecessary check for NULL
 zonelist

On Fri, 1 Aug 2014, Johannes Weiner wrote:

> > > out_of_memory() wants the zonelist that was used during allocation,
> > > not just the random first node's zonelist that's simply picked to
> > > serialize page fault OOM kills system-wide.
> > > 
> > > This would even change how panic_on_oom behaves for page fault OOMs
> > > (in a completely unpredictable way) if we get CONSTRAINED_CPUSET.
> > > 
> > > This change makes no sense to me.
> > > 
> > 
> > Allocations during fault will be constrained by the cpuset's mems, if we 
> > are oom then why would we panic when panic_on_oom == 1?
> 
> Can you please address the concerns I raised?
> 

I see one concern: that panic_on_oom == 1 will not trigger on pagefault 
when constrained by cpusets.  To address that, I'll state that, since 
cpuset-constrained allocations are the allocation context for pagefaults,
panic_on_oom == 1 should not trigger on pagefault when constrained by 
cpusets.

> And please describe user-visible changes in the changelog.
> 

Ok, Andrew please annotate the changelog for 
mm-oom-remove-unnecessary-check-for-null-zonelist.patch by including:

This also causes panic_on_oom == 1 to not panic the machine when the 
pagefault is constrained by the mems of current's cpuset.  That behavior 
agrees with the semantics of the sysctl in Documentation/sysctl/vm.txt.
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