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block: bio_iov_iter_get_pages: pin more pages for multi-segment IOs 

commit <0aa69fd32a5f766e997ca8ab4723c5a1146efa8b>
commit <17d51b10d7773e4618bcac64648f30f12d4078fb>

bio_iov_iter_get_pages() currently only adds pages for the next non-zero
segment from the iov_iter to the bio. That's suboptimal for callers,
which typically try to pin as many pages as fit into the bio. This patch
converts the current bio_iov_iter_get_pages() into a static helper, and
introduces a new helper that allocates as many pages as

 1) fit into the bio,
 2) are present in the iov_iter,
 3) and can be pinned by MM.

Error is returned only if zero pages could be pinned. Because of 3), a
zero return value doesn't necessarily mean all pages have been pinned.
Callers that have to pin every page in the iov_iter must still call this
function in a loop (this is currently the case).

This change matters most for __blkdev_direct_IO_simple(), which calls
bio_iov_iter_get_pages() only once. If it obtains less pages than
requested, it returns a "short write" or "short read", and
__generic_file_write_iter() falls back to buffered writes, which may
lead to data corruption.

Signed-off-by: Chunguang Xu <brookxu@tencent.com>
This commit is contained in:
brookxu 2020-04-24 09:37:45 +08:00 committed by Xiaoming Gao
parent 7c59213786
commit 82ac1bb32d
1 changed files with 32 additions and 3 deletions
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35
block/bio.c
View File

@ -872,14 +872,16 @@ done:
EXPORT_SYMBOL(bio_add_page);
/**
* bio_iov_iter_get_pages - pin user or kernel pages and add them to a bio
* __bio_iov_iter_get_pages - pin user or kernel pages and add them to a bio
* @bio: bio to add pages to
* @iter: iov iterator describing the region to be mapped
*
* Pins as many pages from *iter and appends them to @bio's bvec array. The
* Pins pages from *iter and appends them to @bio's bvec array. The
* pages will have to be released using put_page() when done.
* For multi-segment *iter, this function only adds pages from the
* the next non-empty segment of the iov iterator.
*/
int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
{
unsigned short nr_pages = bio->bi_max_vecs - bio->bi_vcnt, idx;
struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt;
@ -916,6 +918,33 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
iov_iter_advance(iter, size);
return 0;
}
/**
* bio_iov_iter_get_pages - pin user or kernel pages and add them to a bio
* @bio: bio to add pages to
* @iter: iov iterator describing the region to be mapped
*
* Pins pages from *iter and appends them to @bio's bvec array. The
* pages will have to be released using put_page() when done.
* The function tries, but does not guarantee, to pin as many pages as
* fit into the bio, or are requested in *iter, whatever is smaller.
* If MM encounters an error pinning the requested pages, it stops.
* Error is returned only if 0 pages could be pinned.
*/
int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
{
unsigned short orig_vcnt = bio->bi_vcnt;
do {
int ret = __bio_iov_iter_get_pages(bio, iter);
if (unlikely(ret))
return bio->bi_vcnt > orig_vcnt ? 0 : ret;
} while (iov_iter_count(iter) && bio->bi_vcnt < bio->bi_max_vecs);
return 0;
}
EXPORT_SYMBOL_GPL(bio_iov_iter_get_pages);
struct submit_bio_ret {