ext4: don't load the block bitmap for block groups which have no space

Add a short circuit check to ext4_mb_group_group() so that we don't
bother to load the block bitmap for a block group which does not have
any space available.  (Or which does not have enough space until we
are in desperation mode, i.e., when cr == 3.)

Resolves-bug: https://bugzilla.kernel.org/show_bug.cgi?id=45741
Reported-by: mirek@me.com
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 6 insertions, 3 deletions

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 8eae94771c45..3a57975b73cc 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -1862,6 +1862,12 @@ static int ext4_mb_good_group(struct ext4_allocation_context *ac,
 
         BUG_ON(cr < 0 || cr >= 4);
 
+        free = grp->bb_free;
+        if (free == 0)
+                return 0;
+        if (cr <= 2 && free < ac->ac_g_ex.fe_len)
+                return 0;
+
         /* We only do this if the grp has never been initialized */
         if (unlikely(EXT4_MB_GRP_NEED_INIT(grp))) {
                 int ret = ext4_mb_init_group(ac->ac_sb, group);
@@ -1869,10 +1875,7 @@ static int ext4_mb_good_group(struct ext4_allocation_context *ac,
                         return 0;
         }
 
-        free = grp->bb_free;
         fragments = grp->bb_fragments;
-        if (free == 0)
-                return 0;
         if (fragments == 0)
                 return 0;