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Commit b3751e6a authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Darrick J. Wong
Browse files

mm: split ->readpages calls to avoid non-contiguous pages lists 



That way file systems don't have to go spotting for non-contiguous pages
and work around them.  It also kicks off I/O earlier, allowing it to
finish earlier and reduce latency.

Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarDave Chinner <dchinner@redhat.com>
Reviewed-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
parent c534aa3f

mm/readahead.c

+13 −3
Original line number Diff line number Diff line
@@ -140,8 +140,8 @@ static int read_pages(struct address_space *mapping, struct file *filp, 
}



/*

 * __do_page_cache_readahead() actually reads a chunk of disk.  It allocates all

 * the pages first, then submits them all for I/O. This avoids the very bad

 * __do_page_cache_readahead() actually reads a chunk of disk.  It allocates

 * the pages first, then submits them for I/O. This avoids the very bad

 * behaviour which would occur if page allocations are causing VM writeback.

 * We really don't want to intermingle reads and writes like that.

 *
@@ -177,8 +177,18 @@ unsigned int __do_page_cache_readahead(struct address_space *mapping, 
		rcu_read_lock();

		page = radix_tree_lookup(&mapping->i_pages, page_offset);

		rcu_read_unlock();

		if (page && !radix_tree_exceptional_entry(page))

		if (page && !radix_tree_exceptional_entry(page)) {

			/*

			 * Page already present?  Kick off the current batch of

			 * contiguous pages before continuing with the next

			 * batch.

			 */

			if (nr_pages)

				read_pages(mapping, filp, &page_pool, nr_pages,

						gfp_mask);

			nr_pages = 0;

			continue;

		}



		page = __page_cache_alloc(gfp_mask);

		if (!page)