1 files changed, 7 insertions, 8 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index d3df65f83b5c..1bb408f737fb 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -2975,17 +2975,16 @@ again:
         }
         spin_unlock(&block_group->lock);
 
-        num_pages = (int)div64_u64(block_group->key.offset, 1024 * 1024 * 1024);
+        /*
+         * Try to preallocate enough space based on how big the block group is.
+         * Keep in mind this has to include any pinned space which could end up
+         * taking up quite a bit since it's not folded into the other space
+         * cache.
+         */
+        num_pages = (int)div64_u64(block_group->key.offset, 256 * 1024 * 1024);
         if (!num_pages)
                 num_pages = 1;
 
-        /*
-         * Just to make absolutely sure we have enough space, we're going to
-         * preallocate 12 pages worth of space for each block group.  In
-         * practice we ought to use at most 8, but we need extra space so we can
-         * add our header and have a terminator between the extents and the
-         * bitmaps.
-         */
         num_pages *= 16;
         num_pages *= PAGE_CACHE_SIZE;