On Mon, 17 Sep 2012, Jan Kara wrote:
>
> I tripped over a crash in reiserfs which happened due to PageSwapCache
> page being passed to reiserfs_set_page_dirty(). Now it's not that hard to
> make reiserfs_set_page_dirty() check that case but I really wonder: Does it
> make sense to call mapping->a_ops->set_page_dirty() for a PageSwapCache
> page? The page is going to be written via direct IO so from the POV of the
> filesystem there's no need for any dirtiness tracking. Also there are
> several ->set_page_dirty() implementations which will spectacularly crash
> because they do things like page->mapping->host, or call
> __set_page_dirty_buffers() which expects buffer heads in page->private.
> Or what is the reason for calling filesystem's set_page_dirty() function?
This is a question for Mel, really: it used not to call the filesystem.
But my reading of the 3.6 code says that it still will not call the
filesystem, unless the filesystem (only nfs) provides a swap_activate
method, which should be the only case in which SWP_FILE gets set.
And I rather think Mel does want to use the filesystem set_page_dirty
in that case. Am I misreading?
Did you see this on a vanilla kernel? Or is it possible that you have
a private patch merged in, with something else sharing the SWP_FILE bit
(defined in include/linux/swap.h) by mistake?
Hugh
> [PATCH] mm: Remove swap_set_page_dirty()
>
> It doesn't make much sense to call filesystem's ->set_page_dirty() method for
> PageSwapCache page. It will be written through direct IO so filesystem doesn't
> care about its dirtiness and several filesystems actually don't count with such
> pages getting into their ->set_page_dirty() functions.
>
> Signed-off-by: Jan Kara <jack@xxxxxxx>
> ---
> mm/page_io.c | 12 ------------
> mm/swap_state.c | 2 +-
> 2 files changed, 1 insertions(+), 13 deletions(-)
>
> diff --git a/mm/page_io.c b/mm/page_io.c
> index 78eee32..8520a4f 100644
> --- a/mm/page_io.c
> +++ b/mm/page_io.c
> @@ -278,15 +278,3 @@ int swap_readpage(struct page *page)
> out:
> return ret;
> }
> -
> -int swap_set_page_dirty(struct page *page)
> -{
> - struct swap_info_struct *sis = page_swap_info(page);
> -
> - if (sis->flags & SWP_FILE) {
> - struct address_space *mapping = sis->swap_file->f_mapping;
> - 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 0cb36fb..01852cd 100644
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -27,7 +27,7 @@
> */
> 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,
> .migratepage = migrate_page,
> };
>
> --
> 1.7.1
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