In __reserve_bytes() we have 3 repeated calls to btrfs_space_info_used(), one early on as soon as take the space_info's spinlock, another one when we call btrfs_can_overcommit(), which calls btrfs_space_info_used() again, and a final one when we are reserving for a flush emergency. During all these calls we are holding the space_info's spinlock, which is heavily used by the space reservation and flushing code, so it's desirable to make the critical sections as short as possible. So make this more efficient by: 1) Instead of calling btrfs_can_overcommit() call the new variant can_overcommit() which takes the space_info's used space as an argument and pass the value we already computed and have in the 'used' variable; 2) Instead of calling btrfs_space_info_used() with its second argument as false when we are doing a flush emergency, decrement the space_info's bytes_may_use counter from the 'used' variable, as the difference between passing true or false as the second argument to btrfs_space_info_used() is whether or not to include the space_info's bytes_may_use counter in the computation. Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com> Signed-off-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>