fs/block_dev.c: add bdev_read_page() and bdev_write_page()

A block device driver may choose to provide a rw_page operation.  These
will be called when the filesystem is attempting to do page sized I/O to
page cache pages (ie not for direct I/O).  This does preclude I/Os that
are larger than page size, so this may only be a performance gain for
some devices.

Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>
Tested-by: Dheeraj Reddy <dheeraj.reddy@intel.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 12 insertions, 0 deletions

diff --git a/fs/mpage.c b/fs/mpage.c
index 10da0da73017..5f9ed622274f 100644
--- a/fs/mpage.c
+++ b/fs/mpage.c
@@ -269,6 +269,11 @@ do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
 
 alloc_new:
         if (bio == NULL) {
+                if (first_hole == blocks_per_page) {
+                        if (!bdev_read_page(bdev, blocks[0] << (blkbits - 9),
+                                                                page))
+                                goto out;
+                }
                 bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
                                 min_t(int, nr_pages, bio_get_nr_vecs(bdev)),
                                 GFP_KERNEL);
@@ -587,6 +592,13 @@ page_is_mapped:
 
 alloc_new:
         if (bio == NULL) {
+                if (first_unmapped == blocks_per_page) {
+                        if (!bdev_write_page(bdev, blocks[0] << (blkbits - 9),
+                                                                page, wbc)) {
+                                clean_buffers(page, first_unmapped);
+                                goto out;
+                        }
+                }
                 bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
                                 bio_get_nr_vecs(bdev), GFP_NOFS|__GFP_HIGH);
                 if (bio == NULL)