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SubjectRe: [PATCHv5 15/28] ksm: prepare to new THP semantics
On 04/23/2015 11:03 PM, Kirill A. Shutemov wrote:
> We don't need special code to stabilize THP. If you've got reference to
> any subpage of THP it will not be split under you.
>
> New split_huge_page() also accepts tail pages: no need in special code
> to get reference to head page.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Tested-by: Sasha Levin <sasha.levin@oracle.com>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
> mm/ksm.c | 57 ++++++++++-----------------------------------------------
> 1 file changed, 10 insertions(+), 47 deletions(-)
>
> diff --git a/mm/ksm.c b/mm/ksm.c
> index fe09f3ddc912..fb333d8188fc 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -441,20 +441,6 @@ static void break_cow(struct rmap_item *rmap_item)
> up_read(&mm->mmap_sem);
> }
>
> -static struct page *page_trans_compound_anon(struct page *page)
> -{
> - if (PageTransCompound(page)) {
> - struct page *head = compound_head(page);
> - /*
> - * head may actually be splitted and freed from under
> - * us but it's ok here.
> - */
> - if (PageAnon(head))
> - return head;
> - }
> - return NULL;
> -}
> -
> static struct page *get_mergeable_page(struct rmap_item *rmap_item)
> {
> struct mm_struct *mm = rmap_item->mm;
> @@ -470,7 +456,7 @@ static struct page *get_mergeable_page(struct rmap_item *rmap_item)
> page = follow_page(vma, addr, FOLL_GET);
> if (IS_ERR_OR_NULL(page))
> goto out;
> - if (PageAnon(page) || page_trans_compound_anon(page)) {
> + if (PageAnon(page)) {
> flush_anon_page(vma, page, addr);
> flush_dcache_page(page);
> } else {
> @@ -976,33 +962,6 @@ out:
> return err;
> }
>
> -static int page_trans_compound_anon_split(struct page *page)
> -{
> - int ret = 0;
> - struct page *transhuge_head = page_trans_compound_anon(page);
> - if (transhuge_head) {
> - /* Get the reference on the head to split it. */
> - if (get_page_unless_zero(transhuge_head)) {
> - /*
> - * Recheck we got the reference while the head
> - * was still anonymous.
> - */
> - if (PageAnon(transhuge_head))
> - ret = split_huge_page(transhuge_head);
> - else
> - /*
> - * Retry later if split_huge_page run
> - * from under us.
> - */
> - ret = 1;
> - put_page(transhuge_head);
> - } else
> - /* Retry later if split_huge_page run from under us. */
> - ret = 1;
> - }
> - return ret;
> -}
> -
> /*
> * try_to_merge_one_page - take two pages and merge them into one
> * @vma: the vma that holds the pte pointing to page
> @@ -1023,9 +982,6 @@ static int try_to_merge_one_page(struct vm_area_struct *vma,
>
> if (!(vma->vm_flags & VM_MERGEABLE))
> goto out;
> - if (PageTransCompound(page) && page_trans_compound_anon_split(page))
> - goto out;
> - BUG_ON(PageTransCompound(page));
> if (!PageAnon(page))
> goto out;
>
> @@ -1038,6 +994,13 @@ static int try_to_merge_one_page(struct vm_area_struct *vma,
> */
> if (!trylock_page(page))
> goto out;
> +
> + if (PageTransCompound(page)) {
> + err = split_huge_page(page);
> + if (err)
> + goto out_unlock;
> + }
> +
> /*
> * If this anonymous page is mapped only here, its pte may need
> * to be write-protected. If it's mapped elsewhere, all of its
> @@ -1068,6 +1031,7 @@ static int try_to_merge_one_page(struct vm_area_struct *vma,
> }
> }
>
> +out_unlock:
> unlock_page(page);
> out:
> return err;
> @@ -1620,8 +1584,7 @@ next_mm:
> cond_resched();
> continue;
> }
> - if (PageAnon(*page) ||
> - page_trans_compound_anon(*page)) {
> + if (PageAnon(*page)) {
> flush_anon_page(vma, *page, ksm_scan.address);
> flush_dcache_page(*page);
> rmap_item = get_next_rmap_item(slot,
>



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