linux-kernel - Re: [PATCH 07/50] mm: Account for a THP NUMA hinting update as one PTE update

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Date:	Mon, 16 Sep 2013 09:39:59 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Mel Gorman <mgorman@...e.de>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 07/50] mm: Account for a THP NUMA hinting update as one
 PTE update

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@...e.de>
>> ---
>>  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.

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.

IMHO this change makes sense.

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