ext4: check for a good block group before loading buddy pages

This adds a new field in ext4_group_info to cache the largest available
block range in a block group; and don't load the buddy pages until *after*
we've done a sanity check on the block group.

With large allocation requests (e.g., fallocate(), 8MiB) and relatively full
partitions, it's easy to have no block groups with a block extent large
enough to satisfy the input request length.  This currently causes the loop
during cr == 0 in ext4_mb_regular_allocator() to load the buddy bitmap pages
for EVERY block group.  That can be a lot of pages.  The patch below allows
us to call ext4_mb_good_group() BEFORE we load the buddy pages (although we
have check again after we lock the block group).

Addresses-Google-Bug: #2578108
Addresses-Google-Bug: #2704453

Signed-off-by: Curt Wohlgemuth <curtw@google.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 1 insertions, 0 deletions

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index bf938cf7c5f0..d266003cac3e 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1678,6 +1678,7 @@ struct ext4_group_info {
         ext4_grpblk_t   bb_first_free;  /* first free block */
         ext4_grpblk_t   bb_free;        /* total free blocks */
         ext4_grpblk_t   bb_fragments;   /* nr of freespace fragments */
+        ext4_grpblk_t   bb_largest_free_order;/* order of largest frag in BG */
         struct          list_head bb_prealloc_list;
 #ifdef DOUBLE_CHECK
         void            *bb_bitmap;