From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx> Subject: mm: make pagecache tagged lookups return only head pages Patch series "Overhaul multi-page lookups for THP", v4. This THP prep patchset changes several page cache iteration APIs to only return head pages. - It's only possible to tag head pages in the page cache, so only return head pages, not all their subpages. - Factor a lot of common code out of the various batch lookup routines - Add mapping_seek_hole_data() - Unify find_get_entries() and pagevec_lookup_entries() - Make find_get_entries only return head pages, like find_get_entry(). These are only loosely connected, but they seem to make sense together as a series. This patch (of 14): Pagecache tags are used for dirty page writeback. Since dirtiness is tracked on a per-THP basis, we only want to return the head page rather than each subpage of a tagged page. All the filesystems which use huge pages today are in-memory, so there are no tagged huge pages today. Link: https://lkml.kernel.org/r/20201112212641.27837-2-willy@xxxxxxxxxxxxx Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> Reviewed-by: Jan Kara <jack@xxxxxxx> Reviewed-by: William Kucharski <william.kucharski@xxxxxxxxxx> Reviewed-by: Christoph Hellwig <hch@xxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx> Cc: Dave Chinner <dchinner@xxxxxxxxxx> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/filemap.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) --- a/mm/filemap.c~mm-make-pagecache-tagged-lookups-return-only-head-pages +++ a/mm/filemap.c @@ -2062,7 +2062,7 @@ retry: EXPORT_SYMBOL(find_get_pages_contig); /** - * find_get_pages_range_tag - find and return pages in given range matching @tag + * find_get_pages_range_tag - Find and return head pages matching @tag. * @mapping: the address_space to search * @index: the starting page index * @end: The final page index (inclusive) @@ -2070,8 +2070,9 @@ EXPORT_SYMBOL(find_get_pages_contig); * @nr_pages: the maximum number of pages * @pages: where the resulting pages are placed * - * Like find_get_pages, except we only return pages which are tagged with - * @tag. We update @index to index the next page for the traversal. + * Like find_get_pages(), except we only return head pages which are tagged + * with @tag. @index is updated to the index immediately after the last + * page we return, ready for the next iteration. * * Return: the number of pages which were found. */ @@ -2105,9 +2106,9 @@ unsigned find_get_pages_range_tag(struct if (unlikely(page != xas_reload(&xas))) goto put_page; - pages[ret] = find_subpage(page, xas.xa_index); + pages[ret] = page; if (++ret == nr_pages) { - *index = xas.xa_index + 1; + *index = page->index + thp_nr_pages(page); goto out; } continue; _
