Btrfs: fix prealloc under heavy fragmentation conditions
If we are heavily fragmented we will continually try to prealloc the largest
extent size we can every time we call btrfs_reserve_extent. This can be very
expensive when we are heavily fragmented, burning lots of CPU cycles and loops
through the allocator. So instead notice when we get a smaller chunk from the
allocator than what we specified and use this as the new maximum size we try to
allocate. Thanks,
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 5ce55f6..a3e0783 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -9687,6 +9687,7 @@
u64 cur_offset = start;
u64 i_size;
u64 cur_bytes;
+ u64 last_alloc = (u64)-1;
int ret = 0;
bool own_trans = true;
@@ -9703,6 +9704,13 @@
cur_bytes = min(num_bytes, 256ULL * 1024 * 1024);
cur_bytes = max(cur_bytes, min_size);
+ /*
+ * If we are severely fragmented we could end up with really
+ * small allocations, so if the allocator is returning small
+ * chunks lets make its job easier by only searching for those
+ * sized chunks.
+ */
+ cur_bytes = min(cur_bytes, last_alloc);
ret = btrfs_reserve_extent(root, cur_bytes, min_size, 0,
*alloc_hint, &ins, 1, 0);
if (ret) {
@@ -9711,6 +9719,7 @@
break;
}
+ last_alloc = ins.offset;
ret = insert_reserved_file_extent(trans, inode,
cur_offset, ins.objectid,
ins.offset, ins.offset,