Commit e88811bc authored by Jens Axboe's avatar Jens Axboe
Browse files

block: use on-stack page vec for <= UIO_FASTIOV 



Avoid a kmalloc+kfree for each page array, if we only have a few pages
that are mapped. An alloc+free for each IO is quite expensive, and
it's pretty pointless if we're only dealing with 1 or a few vecs.

Use UIO_FASTIOV like we do in other spots to set a sane limit for how
big of an IO we want to avoid allocations for.

Reviewed-by: default avatarChaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 8af870aa

block/blk-map.c

+11 −3
Original line number Diff line number Diff line
@@ -268,12 +268,19 @@ static int bio_map_user_iov(struct request *rq, struct iov_iter *iter, 
	}



	while (iov_iter_count(iter)) {

		struct page **pages;

		struct page **pages, *stack_pages[UIO_FASTIOV];

		ssize_t bytes;

		size_t offs, added = 0;

		int npages;



		bytes = iov_iter_get_pages_alloc2(iter, &pages, LONG_MAX, &offs);

		if (nr_vecs <= ARRAY_SIZE(stack_pages)) {

			pages = stack_pages;

			bytes = iov_iter_get_pages2(iter, pages, LONG_MAX,

							nr_vecs, &offs);

		} else {

			bytes = iov_iter_get_pages_alloc2(iter, &pages,

							LONG_MAX, &offs);

		}

		if (unlikely(bytes <= 0)) {

			ret = bytes ? bytes : -EFAULT;

			goto out_unmap;
@@ -309,6 +316,7 @@ static int bio_map_user_iov(struct request *rq, struct iov_iter *iter, 
		 */

		while (j < npages)

			put_page(pages[j++]);

		if (pages != stack_pages)

			kvfree(pages);

		/* couldn't stuff something into bio? */

		if (bytes) {