On Mon, Jan 24, 2022 at 02:48:32PM +1100, NeilBrown wrote:
> Pages that are written to swap are owned by the MM subsystem - not any
> filesystem.
>
> When such a page is passed to a filesystem to be written out to a
> swap-file, the filesystem handles the data, but the page itself does not
> belong to the filesystem. So calling the filesystem's set_page_dirty
> address_space operation makes no sense. This is for pages in the given
> address space, and a page to be written to swap does not exist in the
> given address space.
>
> So drop swap_set_page_dirty() which calls the address-space's
> set_page_dirty, and alway use __set_page_dirty_no_writeback, which is
> appropriate for pages being swapped out.
Yes, this looks sane to me:
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
>
> Fixes-no-auto-backport: 62c230bc1790 ("mm: add support for a filesystem to activate swap files and use direct_IO for writing swap pages")
> Signed-off-by: NeilBrown <neilb@xxxxxxx>
> ---
> include/linux/swap.h | 1 -
> mm/page_io.c | 14 --------------
> mm/swap_state.c | 2 +-
> 3 files changed, 1 insertion(+), 16 deletions(-)
>
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 3f54a8941c9d..a43929f7033e 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -419,7 +419,6 @@ extern void kswapd_stop(int nid);
>
> #ifdef CONFIG_SWAP
>
> -extern int swap_set_page_dirty(struct page *page);
> int add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
> unsigned long nr_pages, sector_t start_block);
> int generic_swapfile_activate(struct swap_info_struct *, struct file *,
> diff --git a/mm/page_io.c b/mm/page_io.c
> index f8c26092e869..34b12d6f94d7 100644
> --- a/mm/page_io.c
> +++ b/mm/page_io.c
> @@ -438,17 +438,3 @@ int swap_readpage(struct page *page, bool synchronous)
> delayacct_swapin_end();
> return ret;
> }
> -
> -int swap_set_page_dirty(struct page *page)
> -{
> - struct swap_info_struct *sis = page_swap_info(page);
> -
> - if (data_race(sis->flags & SWP_FS_OPS)) {
> - struct address_space *mapping = sis->swap_file->f_mapping;
> -
> - VM_BUG_ON_PAGE(!PageSwapCache(page), page);
> - return mapping->a_ops->set_page_dirty(page);
> - } else {
> - return __set_page_dirty_no_writeback(page);
> - }
> -}
> diff --git a/mm/swap_state.c b/mm/swap_state.c
> index 093ecf864200..d541594be1c3 100644
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -31,7 +31,7 @@
> */
> static const struct address_space_operations swap_aops = {
> .writepage = swap_writepage,
> - .set_page_dirty = swap_set_page_dirty,
> + .set_page_dirty = __set_page_dirty_no_writeback,
> #ifdef CONFIG_MIGRATION
> .migratepage = migrate_page,
> #endif
>
>
---end quoted text---
