On Wed, Sep 07, 2016 at 09:46:07AM -0700, Huang, Ying wrote:
> From: Huang Ying <ying.huang@xxxxxxxxx>
>
> Separates checking whether we can split the huge page from
> split_huge_page_to_list() into a function. This will help to check that
> before splitting the THP (Transparent Huge Page) really.
>
> This will be used for delaying splitting THP during swapping out. Where
> for a THP, we will allocate a swap cluster, add the THP into the swap
> cache, then split the THP. To avoid the unnecessary operations for the
> un-splittable THP, we will check that firstly.
>
> There is no functionality change in this patch.
>
> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Ebru Akagunduz <ebru.akagunduz@xxxxxxxxx>
> Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
> ---
> include/linux/huge_mm.h | 6 ++++++
> mm/huge_memory.c | 13 ++++++++++++-
> 2 files changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index 9b9f65d..a0073e7 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -94,6 +94,7 @@ extern unsigned long thp_get_unmapped_area(struct file *filp,
> extern void prep_transhuge_page(struct page *page);
> extern void free_transhuge_page(struct page *page);
>
> +bool can_split_huge_page(struct page *page);
> int split_huge_page_to_list(struct page *page, struct list_head *list);
> static inline int split_huge_page(struct page *page)
> {
> @@ -176,6 +177,11 @@ static inline void prep_transhuge_page(struct page *page) {}
>
> #define thp_get_unmapped_area NULL
>
> +static inline bool
> +can_split_huge_page(struct page *page)
> +{
BUILD_BUG() should be appropriate here.
> + return false;
> +}
> static inline int
> split_huge_page_to_list(struct page *page, struct list_head *list)
> {
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index fc0d37e..3be5abe 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2016,6 +2016,17 @@ int page_trans_huge_mapcount(struct page *page, int *total_mapcount)
> return ret;
> }
>
> +/* Racy check whether the huge page can be split */
> +bool can_split_huge_page(struct page *page)
> +{
> + int extra_pins = 0;
> +
> + /* Additional pins from radix tree */
> + if (!PageAnon(page))
> + extra_pins = HPAGE_PMD_NR;
> + return total_mapcount(page) == page_count(page) - extra_pins - 1;
> +}
> +
> /*
> * This function splits huge page into normal pages. @page can point to any
> * subpage of huge page to split. Split doesn't change the position of @page.
> @@ -2086,7 +2097,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
> * Racy check if we can split the page, before freeze_page() will
> * split PMDs
> */
> - if (total_mapcount(head) != page_count(head) - extra_pins - 1) {
> + if (!can_split_huge_page(head)) {
> ret = -EBUSY;
> goto out_unlock;
> }
> --
> 2.8.1
>
--
Kirill A. Shutemov
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