Re: [PATCH 07/50] mm: Account for a THP NUMA hinting update as onePTE update

[Mel Gorman]

On Mon, Sep 16, 2013 at 04:54:38PM +0200, Peter Zijlstra wrote:
> On Mon, Sep 16, 2013 at 09:39:59AM -0400, Rik van Riel wrote:
> > On 09/16/2013 08:36 AM, Peter Zijlstra wrote:
> > > On Tue, Sep 10, 2013 at 10:31:47AM +0100, Mel Gorman wrote:
> > >> A THP PMD update is accounted for as 512 pages updated in vmstat.  This is
> > >> large difference when estimating the cost of automatic NUMA balancing and
> > >> can be misleading when comparing results that had collapsed versus split
> > >> THP. This patch addresses the accounting issue.
> > >>
> > >> Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
> > >> ---
> > >>  mm/mprotect.c | 2 +-
> > >>  1 file changed, 1 insertion(+), 1 deletion(-)
> > >>
> > >> diff --git a/mm/mprotect.c b/mm/mprotect.c
> > >> index 94722a4..2bbb648 100644
> > >> --- a/mm/mprotect.c
> > >> +++ b/mm/mprotect.c
> > >> @@ -145,7 +145,7 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
> > >>  				split_huge_page_pmd(vma, addr, pmd);
> > >>  			else if (change_huge_pmd(vma, pmd, addr, newprot,
> > >>  						 prot_numa)) {
> > >> -				pages += HPAGE_PMD_NR;
> > >> +				pages++;
> > > 
> > > But now you're not counting pages anymore..
> > 
> > The migrate statistics still count pages. That makes sense, since the
> > amount of work scales with the amount of memory moved.
> 
> Right.
> 
> > It is just the "number of faults" counters that actually count the
> > number of faults again, instead of the number of pages represented
> > by each fault.
> 
> So you're suggesting s/pages/faults/ or somesuch?
> 

It's really the number of ptes that are updated.

> > IMHO this change makes sense.
> 
> I never said the change didn't make sense as such. Just that we're no
> longer counting pages in change_*_range().

well, it's still a THP page. Is it worth renaming?

-- 
Mel Gorman
SUSE Labs
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