btrfs: preallocate ulist memory for qgroup rsv

When qgroups are enabled, during data reservation, we allocate the
ulist_nodes that track the exact reserved extents with GFP_ATOMIC
unconditionally. This is unnecessary, and we can follow the model
already employed by the struct extent_state we preallocate in the non
qgroups case, which should reduce the risk of allocation failures with
GFP_ATOMIC.

Add a prealloc node to struct ulist which ulist_add will grab when it is
present, and try to allocate it before taking the tree lock while we can
still take advantage of a less strict gfp mask. The lifetime of that
node belongs to the new prealloc field, until it is used, at which point
it belongs to the ulist linked list.

Reviewed-by: Qu Wenruo <[email protected]>
Reviewed-by: Filipe Manana <[email protected]>
Signed-off-by: Boris Burkov <[email protected]>
Reviewed-by: David Sterba <[email protected]>
Signed-off-by: David Sterba <[email protected]>

0 files changed, 0 insertions, 0 deletions