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?
> 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().
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