We can hardcode GFP_NOFS to btrfs_io_bio_alloc, although it means we
change it back from GFP_KERNEL in scrub. I'd rather save a few stack
bytes from not passing the gfp flags in the remaining, more imporatant,
contexts and the bio allocating API now looks more consistent.
Reviewed-by: NLiu Bo <bo.li.liu@oracle.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>