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>

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 8eae947..3a57975 100644 (file)
--- 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;