On Fri, May 01, 2020 at 04:41:19AM +0800, Yang Shi wrote:
> When khugepaged successfully isolated and copied data from old page to
> collapsed THP, the old page is about to be freed if its last mapcount
> is gone. So putting the page back to lru sounds not that productive in
> this case since the page might be isolated by vmscan but it can't be
> reclaimed by vmscan since it can't be unmapped by try_to_unmap() at all.
>
> Actually if khugepaged is the last user of this page so it can be freed
> directly. So, clearing active and unevictable flags, unlocking and
> dropping refcount from isolate instead of calling putback_lru_page().
Any reason putback_lru_page() cannot do it internally? I mean if it is
page_count() == 1, free the page.
>
> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
> ---
> v2: Check mapcount and skip putback lru if the last mapcount is gone
>
> mm/khugepaged.c | 20 ++++++++++++++------
> 1 file changed, 14 insertions(+), 6 deletions(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 0c8d30b..1fdd677 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -559,10 +559,18 @@ void __khugepaged_exit(struct mm_struct *mm)
> static void release_pte_page(struct page *page)
> {
> mod_node_page_state(page_pgdat(page),
> - NR_ISOLATED_ANON + page_is_file_lru(page),
> - -compound_nr(page));
> - unlock_page(page);
> - putback_lru_page(page);
> + NR_ISOLATED_ANON + page_is_file_lru(page), -compound_nr(page));
> +
> + if (total_mapcount(page)) {
> + unlock_page(page);
> + putback_lru_page(page);
> + } else {
> + ClearPageActive(page);
> + ClearPageUnevictable(page);
> + unlock_page(page);
> + /* Drop refcount from isolate */
> + put_page(page);
> + }
> }
>
> static void release_pte_pages(pte_t *pte, pte_t *_pte,
> @@ -771,8 +779,6 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
> } else {
> src_page = pte_page(pteval);
> copy_user_highpage(page, src_page, address, vma);
> - if (!PageCompound(src_page))
> - release_pte_page(src_page);
> /*
> * ptl mostly unnecessary, but preempt has to
> * be disabled to update the per-cpu stats
> @@ -786,6 +792,8 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
> pte_clear(vma->vm_mm, address, _pte);
> page_remove_rmap(src_page, false);
> spin_unlock(ptl);
> + if (!PageCompound(src_page))
> + release_pte_page(src_page);
> free_page_and_swap_cache(src_page);
> }
> }
> --
> 1.8.3.1
>
>
--
Kirill A. Shutemov
