Btrfs: Do more optimal file RA during shrinking and defrag

Signed-off-by: Chris Mason <chris.mason@oracle.com>

fs/btrfs/extent-tree.c

@@ -2263,6 +2263,12 @@ int btrfs_free_block_groups(struct btrfs_fs_info *info)
 	return 0;
 }
 
+static unsigned long calc_ra(unsigned long start, unsigned long last,
+			     unsigned long nr)
+{
+	return min(last, start + nr - 1);
+}
+
 static int noinline relocate_inode_pages(struct inode *inode, u64 start,
 					 u64 len)
 {
@@ -2275,18 +2281,26 @@ static int noinline relocate_inode_pages(struct inode *inode, u64 start,
 	struct page *page;
 	struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
 	struct file_ra_state *ra;
+	unsigned long total_read = 0;
+	unsigned long ra_pages;
 
 	ra = kzalloc(sizeof(*ra), GFP_NOFS);
 
 	mutex_lock(&inode->i_mutex);
 	i = start >> PAGE_CACHE_SHIFT;
 	last_index = (start + len - 1) >> PAGE_CACHE_SHIFT;
 
+	ra_pages = BTRFS_I(inode)->root->fs_info->bdi.ra_pages;
+
 	file_ra_state_init(ra, inode->i_mapping);
-	btrfs_force_ra(inode->i_mapping, ra, NULL, i, last_index);
 	kfree(ra);
 
 	for (; i <= last_index; i++) {
+		if (total_read % ra_pages == 0) {
+			btrfs_force_ra(inode->i_mapping, ra, NULL, i,
+				       calc_ra(i, last_index, ra_pages));
+		}
+		total_read++;
 		page = grab_cache_page(inode->i_mapping, i);
 		if (!page)
 			goto out_unlock;

fs/btrfs/inode.c

@@ -2814,14 +2814,12 @@ unsigned long btrfs_force_ra(struct address_space *mapping,
 			      struct file_ra_state *ra, struct file *file,
 			      pgoff_t offset, pgoff_t last_index)
 {
-	pgoff_t req_size;
+	pgoff_t req_size = last_index - offset + 1;
 
 #if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,23)
-	req_size = last_index - offset + 1;
 	offset = page_cache_readahead(mapping, ra, file, offset, req_size);
 	return offset;
 #else
-	req_size = min(last_index - offset + 1, (pgoff_t)128);
 	page_cache_sync_readahead(mapping, ra, file, offset, req_size);
 	return offset + req_size;
 #endif
@@ -2833,7 +2831,8 @@ int btrfs_defrag_file(struct file *file) {
 	struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
 	struct page *page;
 	unsigned long last_index;
-	unsigned long ra_index = 0;
+	unsigned long ra_pages = root->fs_info->bdi.ra_pages;
+	unsigned long total_read = 0;
 	u64 page_start;
 	u64 page_end;
 	unsigned long i;
@@ -2848,11 +2847,11 @@ int btrfs_defrag_file(struct file *file) {
 	mutex_lock(&inode->i_mutex);
 	last_index = inode->i_size >> PAGE_CACHE_SHIFT;
 	for (i = 0; i <= last_index; i++) {
-		if (i == ra_index) {
-			ra_index = btrfs_force_ra(inode->i_mapping,
-						  &file->f_ra,
-						  file, ra_index, last_index);
+		if (total_read % ra_pages == 0) {
+			btrfs_force_ra(inode->i_mapping, &file->f_ra, file, i,
+				       min(last_index, i + ra_pages - 1));
 		}
+		total_read++;
 		page = grab_cache_page(inode->i_mapping, i);
 		if (!page)
 			goto out_unlock;