ext2: Avoid loading bitmaps for full groups during block allocation

There is no point in loading bitmap for groups which are completely full.
This causes noticeable performance problems (and memory pressure) on small
systems with large full filesystem
(http://marc.info/?l=linux-ext4&m=126843108314310&w=2).

Port of the same ext3 patch.

Signed-off-by: Jan Kara <jack@suse.cz>

diff --git a/fs/ext2/balloc.c b/fs/ext2/balloc.c
index 3cf038c055d7b587290b05bd659624985e9d1056..e8766a3967760f07b210e10e3b879f2c6af62872 100644 (file)
--- a/fs/ext2/balloc.c
+++ b/fs/ext2/balloc.c
@@ -1331,6 +1331,12 @@ retry_alloc:
                        goto io_error;
 
                free_blocks = le16_to_cpu(gdp->bg_free_blocks_count);
+               /*
+                * skip this group (and avoid loading bitmap) if there
+                * are no free blocks
+                */
+               if (!free_blocks)
+                       continue;
                /*
                 * skip this group if the number of
                 * free blocks is less than half of the reservation