__GFP_HIGHMEM is disabled if dax is enabled on brd, however
dax support for brd has been removed since commit (7a862fbbde
"brd: remove dax support"), so restore __GFP_HIGHMEM in
brd_insert_page().
Also remove the no longer applicable comments about DAX and highmem.
Cc: stable@vger.kernel.org
Fixes: 7a862fbbde ("brd: remove dax support")
Signed-off-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
f6b50160a0