[PATCH 3/3] block: use on-stack page vec for <= UIO_FASTIOV
From: Jens Axboe <axboe@kernel.dk>
Date: 2022-08-06 15:20:15
Subsystem:
block layer, the rest · Maintainers:
Jens Axboe, Linus Torvalds
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. Signed-off-by: Jens Axboe <axboe@kernel.dk> --- block/blk-map.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-)
diff --git a/block/blk-map.c b/block/blk-map.c
index 5da03f2614eb..d0ff80a9902e 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_alloc(iter, &pages, LONG_MAX, &offs); + if (nr_vecs < ARRAY_SIZE(stack_pages)) { + pages = stack_pages; + bytes = iov_iter_get_pages(iter, pages, LONG_MAX, + nr_vecs, &offs); + } else { + bytes = iov_iter_get_pages_alloc(iter, &pages, LONG_MAX, + &offs); + } if (unlikely(bytes <= 0)) { ret = bytes ? bytes : -EFAULT; goto out_unmap;
@@ -310,7 +317,8 @@ 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) break;
--
2.35.1