Commit c49f50d1 authored Feb 25, 2021 by Matthew Wilcox (Oracle) Committed by Linus Torvalds Feb 26, 2021

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@infradead.org


Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 6fbd6cf8

mm/filemap.c

+6 −5

Original line number	Diff line number	Diff line
		@@ -2062,7 +2062,7 @@ unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,
		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 address_space mapping, pgoff_t index,
		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;