Re: [PATCH 04/23] page-writeback: Convert write_cache_pages() to use filemap_get_folios_tag()

Dave Chinner
2022-10-18T21:02:40Z

On Thu, Sep 01, 2022 at 03:01:19PM -0700, Vishal Moola (Oracle) wrote:
> Converted function to use folios throughout. This is in preparation for
> the removal of find_get_pages_range_tag().
>
> Signed-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
> ---
> mm/page-writeback.c | 44 +++++++++++++++++++++++---------------------
> 1 file changed, 23 insertions(+), 21 deletions(-)
>
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 032a7bf8d259..087165357a5a 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -2285,15 +2285,15 @@ int write_cache_pages(struct address_space *mapping,
> int ret = 0;
> int done = 0;
> int error;
> - struct pagevec pvec;
> - int nr_pages;
> + struct folio_batch fbatch;
> + int nr_folios;
> pgoff_t index;
> pgoff_t end; /* Inclusive */
> pgoff_t done_index;
> int range_whole = 0;
> xa_mark_t tag;
>
> - pagevec_init(&pvec);
> + folio_batch_init(&fbatch);
> if (wbc->range_cyclic) {
> index = mapping->writeback_index; /* prev offset */
> end = -1;
> @@ -2313,17 +2313,18 @@ int write_cache_pages(struct address_space *mapping,
> while (!done && (index <= end)) {
> int i;
>
> - nr_pages = pagevec_lookup_range_tag(&pvec, mapping, &index, end,
> - tag);
> - if (nr_pages == 0)
> + nr_folios = filemap_get_folios_tag(mapping, &index, end,
> + tag, &fbatch);

This can find and return dirty multi-page folios if the filesystem
enables them in the mapping at instantiation time, right?

> +
> + if (nr_folios == 0)
> break;
>
> - for (i = 0; i < nr_pages; i++) {
> - struct page *page = pvec.pages[i];
> + for (i = 0; i < nr_folios; i++) {
> + struct folio *folio = fbatch.folios[i];
>
> - done_index = page->index;
> + done_index = folio->index;
>
> - lock_page(page);
> + folio_lock(folio);
>
> /*
> * Page truncated or invalidated. We can freely skip it
> @@ -2333,30 +2334,30 @@ int write_cache_pages(struct address_space *mapping,
> * even if there is now a new, dirty page at the same
> * pagecache address.
> */
> - if (unlikely(page->mapping != mapping)) {
> + if (unlikely(folio->mapping != mapping)) {
> continue_unlock:
> - unlock_page(page);
> + folio_unlock(folio);
> continue;
> }
>
> - if (!PageDirty(page)) {
> + if (!folio_test_dirty(folio)) {
> /* someone wrote it for us */
> goto continue_unlock;
> }
>
> - if (PageWriteback(page)) {
> + if (folio_test_writeback(folio)) {
> if (wbc->sync_mode != WB_SYNC_NONE)
> - wait_on_page_writeback(page);
> + folio_wait_writeback(folio);
> else
> goto continue_unlock;
> }
>
> - BUG_ON(PageWriteback(page));
> - if (!clear_page_dirty_for_io(page))
> + BUG_ON(folio_test_writeback(folio));
> + if (!folio_clear_dirty_for_io(folio))
> goto continue_unlock;
>
> trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
> - error = (*writepage)(page, wbc, data);
> + error = writepage(&folio->page, wbc, data);

Yet, IIUC, this treats all folios as if they are single page folios.
i.e. it passes the head page of a multi-page folio to a callback
that will treat it as a single PAGE_SIZE page, because that's all
the writepage callbacks are currently expected to be passed...

So won't this break writeback of dirty multipage folios?

-Dave.
--
Dave Chinner
david@fromorbit.com