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Subject[PATCH v2 51/51] block: bio: pass segments to bio if bio_add_page() is bypassed
Date
Under some situations, such as block direct I/O, we can't use
bio_add_page() for merging pages into multipage bvec, so
a new function is implemented for converting page array into one
segment array, then these cases can benefit from multipage bvec
too.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
block/bio.c | 54 ++++++++++++++++++++++++++++++++++++++++++++++++------
1 file changed, 48 insertions(+), 6 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 436305cde045..e2bcbb842982 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -876,6 +876,41 @@ int bio_add_page(struct bio *bio, struct page *page,
}
EXPORT_SYMBOL(bio_add_page);

+static unsigned convert_to_segs(struct bio* bio, struct page **pages,
+ unsigned char *page_cnt,
+ unsigned nr_pages)
+{
+
+ unsigned idx;
+ unsigned nr_seg = 0;
+ struct request_queue *q = NULL;
+
+ if (bio->bi_bdev)
+ q = bdev_get_queue(bio->bi_bdev);
+
+ if (!q || !blk_queue_cluster(q)) {
+ memset(page_cnt, 0, nr_pages);
+ return nr_pages;
+ }
+
+ page_cnt[nr_seg] = 0;
+ for (idx = 1; idx < nr_pages; idx++) {
+ struct page *pg_s = pages[nr_seg];
+ struct page *pg = pages[idx];
+
+ if (page_to_pfn(pg_s) + page_cnt[nr_seg] + 1 ==
+ page_to_pfn(pg)) {
+ page_cnt[nr_seg]++;
+ } else {
+ page_cnt[++nr_seg] = 0;
+ if (nr_seg < idx)
+ pages[nr_seg] = pg;
+ }
+ }
+
+ return nr_seg + 1;
+}
+
/**
* bio_iov_iter_get_pages - pin user or kernel pages and add them to a bio
* @bio: bio to add pages to
@@ -895,6 +930,8 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
struct page **pages = (struct page **)bv;
size_t offset, diff;
ssize_t size;
+ unsigned short nr_segs;
+ unsigned char page_cnt[nr_pages]; /* at most 256 pages */

size = iov_iter_get_pages(iter, pages, LONG_MAX, nr_pages, &offset);
if (unlikely(size <= 0))
@@ -910,13 +947,18 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
* need to be reflected here as well.
*/
bio->bi_iter.bi_size += size;
- bio->bi_vcnt += nr_pages;
-
diff = (nr_pages * PAGE_SIZE - offset) - size;
- while (nr_pages--) {
- bv[nr_pages].bv_page = pages[nr_pages];
- bv[nr_pages].bv_len = PAGE_SIZE;
- bv[nr_pages].bv_offset = 0;
+
+ /* convert into segments */
+ nr_segs = convert_to_segs(bio, pages, page_cnt, nr_pages);
+ bio->bi_vcnt += nr_segs;
+
+ while (nr_segs--) {
+ unsigned cnt = (unsigned)page_cnt[nr_segs] + 1;
+
+ bv[nr_segs].bv_page = pages[nr_segs];
+ bv[nr_segs].bv_len = PAGE_SIZE * cnt;
+ bv[nr_segs].bv_offset = 0;
}

bv[0].bv_offset += offset;
--
2.9.4
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