Re: [PATCH] mm/lru: Add folio LRU functions

[Yu Zhao <yuzhao@google.com>]

On Thu, May 13, 2021 at 6:28 AM Matthew Wilcox (Oracle)
<willy@infradead.org> wrote:
>
> Handle arbitrary-order folios being added to the LRU.  By definition,
> all pages being added to the LRU were already head or base pages,
> so define page wrappers around folio functions where the original
> page functions involved calling compound_head() to manipulate flags,
> but define folio wrappers around page functions where there's no need to
> call compound_head().  The one thing that does change for those functions
> is calling compound_nr() instead of thp_nr_pages(), in order to handle
> arbitrary-sized folios.
>
> Saves almost 800 bytes of kernel text; no functions grow.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

Reviewed-by: Yu Zhao <yuzhao@google.com>

> ---
>  include/linux/mm_inline.h | 85 +++++++++++++++++++++++++++------------
>  1 file changed, 59 insertions(+), 26 deletions(-)
>
> diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
> index 355ea1ee32bd..c9e05631e565 100644
> --- a/include/linux/mm_inline.h
> +++ b/include/linux/mm_inline.h
> @@ -6,22 +6,27 @@
>  #include <linux/swap.h>
>
>  /**
> - * page_is_file_lru - should the page be on a file LRU or anon LRU?
> - * @page: the page to test
> + * folio_is_file_lru - should the folio be on a file LRU or anon LRU?
> + * @folio: the folio to test
>   *
> - * Returns 1 if @page is a regular filesystem backed page cache page or a lazily
> - * freed anonymous page (e.g. via MADV_FREE).  Returns 0 if @page is a normal
> - * anonymous page, a tmpfs page or otherwise ram or swap backed page.  Used by
> - * functions that manipulate the LRU lists, to sort a page onto the right LRU
> - * list.
> + * Returns 1 if @folio is a regular filesystem backed page cache folio
> + * or a lazily freed anonymous folio (e.g. via MADV_FREE).  Returns 0 if
> + * @folio is a normal anonymous folio, a tmpfs folio or otherwise ram or
> + * swap backed folio.  Used by functions that manipulate the LRU lists,
> + * to sort a folio onto the right LRU list.
>   *
>   * We would like to get this info without a page flag, but the state
> - * needs to survive until the page is last deleted from the LRU, which
> + * needs to survive until the folio is last deleted from the LRU, which
>   * could be as far down as __page_cache_release.
>   */
> +static inline int folio_is_file_lru(struct folio *folio)
> +{
> +       return !folio_swapbacked(folio);
> +}
> +
>  static inline int page_is_file_lru(struct page *page)
>  {
> -       return !PageSwapBacked(page);
> +       return folio_is_file_lru(page_folio(page));
>  }
>
>  static __always_inline void update_lru_size(struct lruvec *lruvec,
> @@ -42,66 +47,94 @@ static __always_inline void update_lru_size(struct lruvec *lruvec,
>   * __clear_page_lru_flags - clear page lru flags before releasing a page
>   * @page: the page that was on lru and now has a zero reference
>   */
> -static __always_inline void __clear_page_lru_flags(struct page *page)
> +static __always_inline void __folio_clear_lru_flags(struct folio *folio)
>  {
> -       VM_BUG_ON_PAGE(!PageLRU(page), page);
> +       VM_BUG_ON_FOLIO(!folio_lru(folio), folio);
>
> -       __ClearPageLRU(page);
> +       __folio_clear_lru_flag(folio);
>
>         /* this shouldn't happen, so leave the flags to bad_page() */
> -       if (PageActive(page) && PageUnevictable(page))
> +       if (folio_active(folio) && folio_unevictable(folio))
>                 return;
>
> -       __ClearPageActive(page);
> -       __ClearPageUnevictable(page);
> +       __folio_clear_active_flag(folio);
> +       __folio_clear_unevictable_flag(folio);
> +}
> +
> +static __always_inline void __clear_page_lru_flags(struct page *page)
> +{
> +       __folio_clear_lru_flags(page_folio(page));
>  }
>
>  /**
> - * page_lru - which LRU list should a page be on?
> - * @page: the page to test
> + * folio_lru_list - which LRU list should a folio be on?
> + * @folio: the folio to test
>   *
> - * Returns the LRU list a page should be on, as an index
> + * Returns the LRU list a folio should be on, as an index
>   * into the array of LRU lists.
>   */
> -static __always_inline enum lru_list page_lru(struct page *page)
> +static __always_inline enum lru_list folio_lru_list(struct folio *folio)
>  {
>         enum lru_list lru;
>
> -       VM_BUG_ON_PAGE(PageActive(page) && PageUnevictable(page), page);
> +       VM_BUG_ON_FOLIO(folio_active(folio) && folio_unevictable(folio), folio);
>
> -       if (PageUnevictable(page))
> +       if (folio_unevictable(folio))
>                 return LRU_UNEVICTABLE;
>
> -       lru = page_is_file_lru(page) ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON;
> -       if (PageActive(page))
> +       lru = folio_is_file_lru(folio) ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON;
> +       if (folio_active(folio))
>                 lru += LRU_ACTIVE;
>
>         return lru;
>  }
>
> +static __always_inline enum lru_list page_lru(struct page *page)
> +{
> +       return folio_lru_list(page_folio(page));
> +}
> +
>  static __always_inline void add_page_to_lru_list(struct page *page,
>                                 struct lruvec *lruvec)
>  {
>         enum lru_list lru = page_lru(page);
>
> -       update_lru_size(lruvec, lru, page_zonenum(page), thp_nr_pages(page));
> +       update_lru_size(lruvec, lru, page_zonenum(page), compound_nr(page));
>         list_add(&page->lru, &lruvec->lists[lru]);
>  }
>
> +static __always_inline void folio_add_to_lru_list(struct folio *folio,
> +                               struct lruvec *lruvec)
> +{
> +       add_page_to_lru_list(&folio->page, lruvec);
> +}
> +
>  static __always_inline void add_page_to_lru_list_tail(struct page *page,
>                                 struct lruvec *lruvec)
>  {
>         enum lru_list lru = page_lru(page);
>
> -       update_lru_size(lruvec, lru, page_zonenum(page), thp_nr_pages(page));
> +       update_lru_size(lruvec, lru, page_zonenum(page), compound_nr(page));
>         list_add_tail(&page->lru, &lruvec->lists[lru]);
>  }
>
> +static __always_inline void folio_add_to_lru_list_tail(struct folio *folio,
> +                               struct lruvec *lruvec)
> +{
> +       add_page_to_lru_list_tail(&folio->page, lruvec);
> +}
> +
>  static __always_inline void del_page_from_lru_list(struct page *page,
>                                 struct lruvec *lruvec)
>  {
>         list_del(&page->lru);
>         update_lru_size(lruvec, page_lru(page), page_zonenum(page),
> -                       -thp_nr_pages(page));
> +                       -compound_nr(page));
> +}
> +
> +static __always_inline void folio_del_from_lru_list(struct folio *folio,
> +                               struct lruvec *lruvec)
> +{
> +       del_page_from_lru_list(&folio->page, lruvec);
>  }
>  #endif
> --
> 2.30.2
>