@@ -1591,9 +1591,6 @@ 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 +1605,32 @@ 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);
My fix Btrfs: fix merge delalloc logic only fixed half of the problems, it didn't fix the case where we have two large extents on either side and then join them together with a new small extent. We need to instead keep track of how many extents we have accounted for with each side of the new extent, and then see how many extents we need for the new large extent. If they match then we know we need to keep our reservation, otherwise we need to drop our reservation. This shows up with a case like this [BTRFS_MAX_EXTENT_SIZE+4K][4K HOLE][BTRFS_MAX_EXTENT_SIZE+4K] Previously the logic would have said that the number extents required for the new size (3) is larger than the number of extents required for the largest side (2) therefore we need to keep our reservation. But this isn't the case, since both sides require a reservation of 2 which leads to 4 for the whole range currently reserved, but we only need 3, so we need to drop one of the reservations. This fixes the last accounting problem. Thanks, Signed-off-by: Josef Bacik <jbacik@fb.com> --- -Same as the v2 of "Btrfs: fix merge delalloc logic" except it was rebased onto Chris's integration branch as an incremental to keep the history clean. fs/btrfs/inode.c | 28 ++++++++++++++++++++++------ 1 file changed, 22 insertions(+), 6 deletions(-)