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SubjectRe: [PATCH -mmotm-2009-12-10-17-19] Prevent churning of zero page in LRU list.
On Mon, 28 Dec 2009 11:53:15 +0900
Minchan Kim <minchan.kim@gmail.com> wrote:

>
> VM doesn't add zero page to LRU list.
> It means zero page's churning in LRU list is pointless.
>
> As a matter of fact, zero page can't be promoted by mark_page_accessed
> since it doesn't have PG_lru.
>
> This patch prevent unecessary mark_page_accessed call of zero page
> alghouth caller want FOLL_TOUCH.
>
> Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

> ---
> mm/memory.c | 7 ++++---
> 1 files changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index 09e4b1b..485f727 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1152,6 +1152,7 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
> spinlock_t *ptl;
> struct page *page;
> struct mm_struct *mm = vma->vm_mm;
> + int zero_pfn = 0;
>
> page = follow_huge_addr(mm, address, flags & FOLL_WRITE);
> if (!IS_ERR(page)) {
> @@ -1196,15 +1197,15 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
>
> page = vm_normal_page(vma, address, pte);
> if (unlikely(!page)) {
> - if ((flags & FOLL_DUMP) ||
> - !is_zero_pfn(pte_pfn(pte)))
> + zero_pfn = is_zero_pfn(pte_pfn(pte));
> + if ((flags & FOLL_DUMP) || !zero_pfn )
> goto bad_page;
> page = pte_page(pte);
> }
>
> if (flags & FOLL_GET)
> get_page(page);
> - if (flags & FOLL_TOUCH) {
> + if (flags & FOLL_TOUCH && !zero_pfn) {
> if ((flags & FOLL_WRITE) &&
> !pte_dirty(pte) && !PageDirty(page))
> set_page_dirty(page);
> --
> 1.5.6.3
>
>
> --
> Kind regards,
> Minchan Kim
>
> --
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>



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