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SubjectRe: [PATCH 04/18] mm: numa: Do not migrate or account for hinting faults on the zero page
On Wed, Jul 17, 2013 at 01:00:53PM +0200, Peter Zijlstra wrote:
> On Mon, Jul 15, 2013 at 04:20:06PM +0100, Mel Gorman wrote:
> > The zero page is not replicated between nodes and is often shared
> > between processes. The data is read-only and likely to be cached in
> > local CPUs if heavily accessed meaning that the remote memory access
> > cost is less of a concern. This patch stops accounting for numa hinting
> > faults on the zero page in both terms of counting faults and scheduling
> > tasks on nodes.
> >
> > Signed-off-by: Mel Gorman <mgorman@suse.de>
> > ---
> > mm/huge_memory.c | 9 +++++++++
> > mm/memory.c | 7 ++++++-
> > 2 files changed, 15 insertions(+), 1 deletion(-)
> >
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > index e4a79fa..ec938ed 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -1302,6 +1302,15 @@ int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
> >
> > page = pmd_page(pmd);
> > get_page(page);
> > +
> > + /*
> > + * Do not account for faults against the huge zero page. The read-only
> > + * data is likely to be read-cached on the local CPUs and it is less
> > + * useful to know about local versus remote hits on the zero page.
> > + */
> > + if (is_huge_zero_pfn(page_to_pfn(page)))
> > + goto clear_pmdnuma;
> > +
> > src_nid = numa_node_id();
> > count_vm_numa_event(NUMA_HINT_FAULTS);
> > if (src_nid == page_to_nid(page))
>
> And because of:
>
> 5918d10 thp: fix huge zero page logic for page with pfn == 0
>

Yes. Thanks.

--
Mel Gorman
SUSE Labs


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