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SubjectRe: [PATCHv4 19/24] thp, mm: use migration entries to freeze page counts on split
Date
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> writes:

> Currently, we rely on compound_lock() to get page counts stable on
> splitting page refcounting. To get it work we also take the lock on
> get_page() and put_page() which is hot path.
>
> This patch rework splitting code to setup migration entries to stabilaze
> page count/mapcount before distribute refcounts. It means we don't need
> to compound lock in get_page()/put_page().
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---
> include/linux/migrate.h | 3 +
> include/linux/mm.h | 1 +
> include/linux/pagemap.h | 9 ++-
> mm/huge_memory.c | 188 +++++++++++++++++++++++++++++++++++-------------
> mm/internal.h | 26 +++++--
> mm/migrate.c | 79 +++++++++++---------
> mm/rmap.c | 21 ------
> 7 files changed, 218 insertions(+), 109 deletions(-)
>
> diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> index 78baed5f2952..b9bc86c24829 100644
> --- a/include/linux/migrate.h
> +++ b/include/linux/migrate.h
> @@ -43,6 +43,9 @@ extern int migrate_page_move_mapping(struct address_space *mapping,
> struct page *newpage, struct page *page,
> struct buffer_head *head, enum migrate_mode mode,
> int extra_count);
> +extern int __remove_migration_pte(struct page *new, struct vm_area_struct *vma,
> + unsigned long addr, pte_t *ptep, struct page *old);
> +
> #else
>
> static inline void putback_movable_pages(struct list_head *l) {}
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 28aeae6e553b..43a9993f1333 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -981,6 +981,7 @@ extern struct address_space *page_mapping(struct page *page);
> /* Neutral page->mapping pointer to address_space or anon_vma or other */
> static inline void *page_rmapping(struct page *page)
> {
> + page = compound_head(page);
> return (void *)((unsigned long)page->mapping & ~PAGE_MAPPING_FLAGS);
> }
>

The above hunk is related to this patch ?. Are we calling page_rmapping
on tail pages now ? If so it needs additonal comment why we handle them
differently now. Or split it to a seperate patch ?

-aneesh



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