readahead: convert ext3/ext4 invocations

Convert ext3/ext4 dir reads to use on-demand readahead.

Readahead for dirs operates _not_ on file level, but on blockdev level.  This
makes a difference when the data blocks are not continuous.  And the read
routine is somehow opaque: there's no handy info about the status of current
page.  So a simplified call scheme is employed: to call into readahead
whenever the current page falls out of readahead windows.

Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
Cc: Steven Pratt <slpratt@austin.ibm.com>
Cc: Ram Pai <linuxram@us.ibm.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/ext3/dir.c

@@ -136,12 +136,14 @@ static int ext3_readdir(struct file * filp,
 		err = ext3_get_blocks_handle(NULL, inode, blk, 1,
 						&map_bh, 0, 0);
 		if (err > 0) {
-			page_cache_readahead(sb->s_bdev->bd_inode->i_mapping,
-				&filp->f_ra,
-				filp,
-				map_bh.b_blocknr >>
-					(PAGE_CACHE_SHIFT - inode->i_blkbits),
-				1);
+			pgoff_t index = map_bh.b_blocknr >>
+					(PAGE_CACHE_SHIFT - inode->i_blkbits);
+			if (!ra_has_index(&filp->f_ra, index))
+				page_cache_readahead_ondemand(
+					sb->s_bdev->bd_inode->i_mapping,
+					&filp->f_ra, filp,
+					NULL, index, 1);
+			filp->f_ra.prev_index = index;
 			bh = ext3_bread(NULL, inode, blk, 0, &err);
 		}
 

fs/ext4/dir.c

@@ -135,12 +135,14 @@ static int ext4_readdir(struct file * filp,
 		map_bh.b_state = 0;
 		err = ext4_get_blocks_wrap(NULL, inode, blk, 1, &map_bh, 0, 0);
 		if (err > 0) {
-			page_cache_readahead(sb->s_bdev->bd_inode->i_mapping,
-				&filp->f_ra,
-				filp,
-				map_bh.b_blocknr >>
-					(PAGE_CACHE_SHIFT - inode->i_blkbits),
-				1);
+			pgoff_t index = map_bh.b_blocknr >>
+					(PAGE_CACHE_SHIFT - inode->i_blkbits);
+			if (!ra_has_index(&filp->f_ra, index))
+				page_cache_readahead_ondemand(
+					sb->s_bdev->bd_inode->i_mapping,
+					&filp->f_ra, filp,
+					NULL, index, 1);
+			filp->f_ra.prev_index = index;
 			bh = ext4_bread(NULL, inode, blk, 0, &err);
 		}