linux-kernel - Re: [PATCH 14/15] mm: numa: Flush TLB if NUMA hinting faults race with PTE scan update

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Date:	Tue, 3 Dec 2013 23:46:37 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Rik van Riel <riel@...hat.com>
Cc:	Alex Thorlton <athorlton@....com>, Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 14/15] mm: numa: Flush TLB if NUMA hinting faults race
 with PTE scan update

On Tue, Dec 03, 2013 at 06:07:06PM -0500, Rik van Riel wrote:
> On 12/03/2013 03:52 AM, Mel Gorman wrote:
> > NUMA PTE updates and NUMA PTE hinting faults can race against each other. The
> > setting of the NUMA bit defers the TLB flush to reduce overhead. NUMA
> > hinting faults do not flush the TLB as X86 at least does not cache TLB
> > entries for !present PTEs. However, in the event that the two race a NUMA
> > hinting fault may return with the TLB in an inconsistent state between
> > different processors. This patch detects potential for races between the
> > NUMA PTE scanner and fault handler and will flush the TLB for the affected
> > range if there is a race.
> > 
> > Signed-off-by: Mel Gorman <mgorman@...e.de>
> 
> > diff --git a/mm/migrate.c b/mm/migrate.c
> > index 5dfd552..ccc814b 100644
> > --- a/mm/migrate.c
> > +++ b/mm/migrate.c
> > @@ -1662,6 +1662,39 @@ void wait_migrate_huge_page(struct anon_vma *anon_vma, pmd_t *pmd)
> >  	smp_rmb();
> >  }
> >  
> > +unsigned long numa_fault_prepare(struct mm_struct *mm)
> > +{
> > +	/* Paired with task_numa_work */
> > +	smp_rmb();
> > +	return mm->numa_next_reset;
> > +}
> 
> The patch that introduces mm->numa_next_reset, and the
> patch that increments it, seem to be missing from your
> series...
> 

Damn. s/numa_next_reset/numa_next_scan/ in that patch

-- 
Mel Gorman
SUSE Labs
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