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: Chaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/block/blk-map.c b/block/blk-map.c
index 16153fd..f376887 100644
--- a/block/blk-map.c
+++ b/block/blk-map.c
@@ -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;
@@ -309,7 +316,8 @@ static int bio_map_user_iov(struct request *rq, struct iov_iter *iter,
*/
while (j < npages)
put_page(pages[j++]);
- kvfree(pages);
+ if (pages != stack_pages)
+ kvfree(pages);
/* couldn't stuff something into bio? */
if (bytes) {
iov_iter_revert(iter, bytes);
