Re: [PATCHv6 01/36] mm, proc: adjust PSS calculation

[Vlastimil Babka]

On 06/03/2015 07:05 PM, Kirill A. Shutemov wrote:
> With new refcounting all subpages of the compound page are not nessessary
> have the same mapcount. We need to take into account mapcount of every
> sub-page.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Tested-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
> Acked-by: Jerome Marchand <jmarchan@xxxxxxxxxx>
> Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
> ---
>   fs/proc/task_mmu.c | 48 +++++++++++++++++++++++++++++++-----------------
>   1 file changed, 31 insertions(+), 17 deletions(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 58be92e11939..f9b285761bc0 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -449,9 +449,10 @@ struct mem_size_stats {
>   };
>
>   static void smaps_account(struct mem_size_stats *mss, struct page *page,
> -		unsigned long size, bool young, bool dirty)
> +		bool compound, bool young, bool dirty)
>   {
> -	int mapcount;
> +	int i, nr = compound ? HPAGE_PMD_NR : 1;
> +	unsigned long size = nr * PAGE_SIZE;
>
>   	if (PageAnon(page))
>   		mss->anonymous += size;
> @@ -460,23 +461,36 @@ static void smaps_account(struct mem_size_stats *mss, struct page *page,
>   	/* Accumulate the size in pages that have been accessed. */
>   	if (young || PageReferenced(page))
>   		mss->referenced += size;
> -	mapcount = page_mapcount(page);
> -	if (mapcount >= 2) {
> -		u64 pss_delta;
>
> -		if (dirty || PageDirty(page))
> -			mss->shared_dirty += size;
> -		else
> -			mss->shared_clean += size;
> -		pss_delta = (u64)size << PSS_SHIFT;
> -		do_div(pss_delta, mapcount);
> -		mss->pss += pss_delta;
> -	} else {
> +	/*
> +	 * page_count(page) == 1 guarantees the page is mapped exactly once.
> +	 * If any subpage of the compound page mapped with PTE it would elevate
> +	 * page_count().
> +	 */
> +	if (page_count(page) == 1) {
>   		if (dirty || PageDirty(page))
>   			mss->private_dirty += size;
>   		else
>   			mss->private_clean += size;
> -		mss->pss += (u64)size << PSS_SHIFT;

Deleting the line above was a mistake, right?

> +		return;
> +	}
> +
> +	for (i = 0; i < nr; i++, page++) {
> +		int mapcount = page_mapcount(page);
> +
> +		if (mapcount >= 2) {
> +			if (dirty || PageDirty(page))
> +				mss->shared_dirty += PAGE_SIZE;
> +			else
> +				mss->shared_clean += PAGE_SIZE;
> +			mss->pss += (PAGE_SIZE << PSS_SHIFT) / mapcount;
> +		} else {
> +			if (dirty || PageDirty(page))
> +				mss->private_dirty += PAGE_SIZE;
> +			else
> +				mss->private_clean += PAGE_SIZE;
> +			mss->pss += PAGE_SIZE << PSS_SHIFT;
> +		}
>   	}
>   }
>
> @@ -500,7 +514,8 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
>
>   	if (!page)
>   		return;
> -	smaps_account(mss, page, PAGE_SIZE, pte_young(*pte), pte_dirty(*pte));
> +
> +	smaps_account(mss, page, false, pte_young(*pte), pte_dirty(*pte));
>   }
>
>   #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> @@ -516,8 +531,7 @@ static void smaps_pmd_entry(pmd_t *pmd, unsigned long addr,
>   	if (IS_ERR_OR_NULL(page))
>   		return;
>   	mss->anonymous_thp += HPAGE_PMD_SIZE;
> -	smaps_account(mss, page, HPAGE_PMD_SIZE,
> -			pmd_young(*pmd), pmd_dirty(*pmd));
> +	smaps_account(mss, page, true, pmd_young(*pmd), pmd_dirty(*pmd));
>   }
>   #else
>   static void smaps_pmd_entry(pmd_t *pmd, unsigned long addr,

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