1 files changed, 30 insertions, 27 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 97b601bec326..bb74a4181075 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1542,30 +1542,17 @@ static void btrfs_split_extent_hook(struct inode *inode,
                 u64 new_size;
 
                 /*
-                 * We need the largest size of the remaining extent to see if we
-                 * need to add a new outstanding extent.  Think of the following
-                 * case
-                 *
-                 * [MEAX_EXTENT_SIZEx2 - 4k][4k]
-                 *
-                 * The new_size would just be 4k and we'd think we had enough
-                 * outstanding extents for this if we only took one side of the
-                 * split, same goes for the other direction.  We need to see if
-                 * the larger size still is the same amount of extents as the
-                 * original size, because if it is we need to add a new
-                 * outstanding extent.  But if we split up and the larger size
-                 * is less than the original then we are good to go since we've
-                 * already accounted for the extra extent in our original
-                 * accounting.
+                 * See the explanation in btrfs_merge_extent_hook, the same
+                 * applies here, just in reverse.
                  */
                 new_size = orig->end - split + 1;
-                if ((split - orig->start) > new_size)
-                        new_size = split - orig->start;
-
-                num_extents = div64_u64(size + BTRFS_MAX_EXTENT_SIZE - 1,
+                num_extents = div64_u64(new_size + BTRFS_MAX_EXTENT_SIZE - 1,
                                         BTRFS_MAX_EXTENT_SIZE);
-                if (div64_u64(new_size + BTRFS_MAX_EXTENT_SIZE - 1,
-                              BTRFS_MAX_EXTENT_SIZE) < num_extents)
+                new_size = split - orig->start;
+                num_extents += div64_u64(new_size + BTRFS_MAX_EXTENT_SIZE - 1,
+                                        BTRFS_MAX_EXTENT_SIZE);
+                if (div64_u64(size + BTRFS_MAX_EXTENT_SIZE - 1,
+                              BTRFS_MAX_EXTENT_SIZE) >= num_extents)
                         return;
         }
 
@@ -1591,9 +1578,6 @@ static void btrfs_merge_extent_hook(struct inode *inode,
         if (!(other->state & EXTENT_DELALLOC))
                 return;
 
-        old_size = other->end - other->start + 1;
-        if (old_size < (new->end - new->start + 1))
-                old_size = (new->end - new->start + 1);
         if (new->start > other->start)
                 new_size = new->end - other->start + 1;
         else
@@ -1608,13 +1592,32 @@ static void btrfs_merge_extent_hook(struct inode *inode,
         }
 
         /*
-         * If we grew by another max_extent, just return, we want to keep that
-         * reserved amount.
+         * We have to add up either side to figure out how many extents were
+         * accounted for before we merged into one big extent.  If the number of
+         * extents we accounted for is <= the amount we need for the new range
+         * then we can return, otherwise drop.  Think of it like this
+         *
+         * [ 4k][MAX_SIZE]
+         *
+         * So we've grown the extent by a MAX_SIZE extent, this would mean we
+         * need 2 outstanding extents, on one side we have 1 and the other side
+         * we have 1 so they are == and we can return.  But in this case
+         *
+         * [MAX_SIZE+4k][MAX_SIZE+4k]
+         *
+         * Each range on their own accounts for 2 extents, but merged together
+         * they are only 3 extents worth of accounting, so we need to drop in
+         * this case.
          */
+        old_size = other->end - other->start + 1;
         num_extents = div64_u64(old_size + BTRFS_MAX_EXTENT_SIZE - 1,
                                 BTRFS_MAX_EXTENT_SIZE);
+        old_size = new->end - new->start + 1;
+        num_extents += div64_u64(old_size + BTRFS_MAX_EXTENT_SIZE - 1,
+                                 BTRFS_MAX_EXTENT_SIZE);
+
         if (div64_u64(new_size + BTRFS_MAX_EXTENT_SIZE - 1,
-                      BTRFS_MAX_EXTENT_SIZE) > num_extents)
+                      BTRFS_MAX_EXTENT_SIZE) >= num_extents)
                 return;
 
         spin_lock(&BTRFS_I(inode)->lock);