Re: [PATCH 7/8] mm: drop page_index/page_file_offset and convert swap helpers to use folio

[Barry Song]

On Thu, Apr 18, 2024 at 4:12 AM Kairui Song <ryncsn@xxxxxxxxx> wrote:
>
> From: Kairui Song <kasong@xxxxxxxxxxx>
>
> When applied on swap cache pages, page_index / page_file_offset was used
> to retrieve the swap cache index or swap file offset of a page, and they
> have their folio equivalence version: folio_index / folio_file_pos.
>
> We have eliminated all users for page_index / page_file_offset, everything
> is using folio_index / folio_file_pos now, so remove the old helpers.
>
> Then convert the implementation of folio_index / folio_file_pos to
> to use folio natively.
>
> After this commit, all users that might encounter mixed usage of swap
> cache and page cache will only use following two helpers:
>
> folio_index (calls __folio_swap_cache_index)
> folio_file_pos (calls __folio_swap_file_pos)
>
> The offset in swap file and index in swap cache is still basically the
> same thing at this moment, but will be different in following commits.
>
> Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>

Hi Kairui, thanks !

I also find it rather odd that folio_file_page() is utilized for both
swp and file.

mm/memory.c <<do_swap_page>>
             page = folio_file_page(folio, swp_offset(entry));
mm/swap_state.c <<swapin_readahead>>
             return folio_file_page(folio, swp_offset(entry));
mm/swapfile.c <<unuse_pte>>
             page = folio_file_page(folio, swp_offset(entry));

Do you believe it's worthwhile to tidy up?

> ---
>  include/linux/mm.h      | 13 -------------
>  include/linux/pagemap.h | 19 +++++++++----------
>  mm/swapfile.c           | 13 +++++++++----
>  3 files changed, 18 insertions(+), 27 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 0436b919f1c7..797480e76c9c 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2245,19 +2245,6 @@ static inline void *folio_address(const struct folio *folio)
>         return page_address(&folio->page);
>  }
>
> -extern pgoff_t __page_file_index(struct page *page);
> -
> -/*
> - * Return the pagecache index of the passed page.  Regular pagecache pages
> - * use ->index whereas swapcache pages use swp_offset(->private)
> - */
> -static inline pgoff_t page_index(struct page *page)
> -{
> -       if (unlikely(PageSwapCache(page)))
> -               return __page_file_index(page);
> -       return page->index;
> -}
> -
>  /*
>   * Return true only if the page has been allocated with
>   * ALLOC_NO_WATERMARKS and the low watermark was not
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index 2df35e65557d..313f3144406e 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -780,7 +780,7 @@ static inline struct page *grab_cache_page_nowait(struct address_space *mapping,
>                         mapping_gfp_mask(mapping));
>  }
>
> -#define swapcache_index(folio) __page_file_index(&(folio)->page)
> +extern pgoff_t __folio_swap_cache_index(struct folio *folio);
>
>  /**
>   * folio_index - File index of a folio.
> @@ -795,9 +795,9 @@ static inline struct page *grab_cache_page_nowait(struct address_space *mapping,
>   */
>  static inline pgoff_t folio_index(struct folio *folio)
>  {
> -        if (unlikely(folio_test_swapcache(folio)))
> -                return swapcache_index(folio);
> -        return folio->index;
> +       if (unlikely(folio_test_swapcache(folio)))
> +               return __folio_swap_cache_index(folio);
> +       return folio->index;
>  }
>
>  /**
> @@ -920,11 +920,6 @@ static inline loff_t page_offset(struct page *page)
>         return ((loff_t)page->index) << PAGE_SHIFT;
>  }
>
> -static inline loff_t page_file_offset(struct page *page)
> -{
> -       return ((loff_t)page_index(page)) << PAGE_SHIFT;
> -}
> -
>  /**
>   * folio_pos - Returns the byte position of this folio in its file.
>   * @folio: The folio.
> @@ -934,6 +929,8 @@ static inline loff_t folio_pos(struct folio *folio)
>         return page_offset(&folio->page);
>  }
>
> +extern loff_t __folio_swap_file_pos(struct folio *folio);
> +
>  /**
>   * folio_file_pos - Returns the byte position of this folio in its file.
>   * @folio: The folio.
> @@ -943,7 +940,9 @@ static inline loff_t folio_pos(struct folio *folio)
>   */
>  static inline loff_t folio_file_pos(struct folio *folio)
>  {
> -       return page_file_offset(&folio->page);
> +       if (unlikely(folio_test_swapcache(folio)))
> +               return __folio_swap_file_pos(folio);
> +       return ((loff_t)folio->index << PAGE_SHIFT);
>  }
>
>  /*
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 4919423cce76..0c36a5c2400f 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -3419,12 +3419,17 @@ struct address_space *swapcache_mapping(struct folio *folio)
>  }
>  EXPORT_SYMBOL_GPL(swapcache_mapping);
>
> -pgoff_t __page_file_index(struct page *page)
> +pgoff_t __folio_swap_cache_index(struct folio *folio)
>  {
> -       swp_entry_t swap = page_swap_entry(page);
> -       return swp_offset(swap);
> +       return swp_offset(folio->swap);
>  }
> -EXPORT_SYMBOL_GPL(__page_file_index);
> +EXPORT_SYMBOL_GPL(__folio_swap_cache_index);
> +
> +loff_t __folio_swap_file_pos(struct folio *folio)
> +{
> +       return swap_file_pos(folio->swap);
> +}
> +EXPORT_SYMBOL_GPL(__folio_swap_file_pos);
>
>  /*
>   * add_swap_count_continuation - called when a swap count is duplicated
> --
> 2.44.0
>

Thanks
Barry