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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>
pull/520/merge
Jens Axboe 2022-08-05 16:44:34 -06:00
parent 8af870aa5b
commit e88811bc43
1 changed files with 11 additions and 3 deletions
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14
block/blk-map.c
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@ -268,12 +268,19 @@ static int bio_map_user_iov(struct request *rq, struct iov_iter *iter,
} }
while (iov_iter_count(iter)) { while (iov_iter_count(iter)) {
struct page **pages; struct page **pages, *stack_pages[UIO_FASTIOV];
ssize_t bytes; ssize_t bytes;
size_t offs, added = 0; size_t offs, added = 0;
int npages; 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)) { if (unlikely(bytes <= 0)) {
ret = bytes ? bytes : -EFAULT; ret = bytes ? bytes : -EFAULT;
goto out_unmap; goto out_unmap;
@ -309,7 +316,8 @@ static int bio_map_user_iov(struct request *rq, struct iov_iter *iter,
*/ */
while (j < npages) while (j < npages)
put_page(pages[j++]); put_page(pages[j++]);
kvfree(pages); if (pages != stack_pages)
kvfree(pages);
/* couldn't stuff something into bio? */ /* couldn't stuff something into bio? */
if (bytes) { if (bytes) {
iov_iter_revert(iter, bytes); iov_iter_revert(iter, bytes);