[PATCH v4 1/2] block: add folio awareness instead of looping through pages

[Kundan Kumar <kundan.kumar@xxxxxxxxxxx>]

Add a bigger size from folio to bio and skip merge processing for pages.

Fetch the offset of page within a folio. Depending on the size of folio
and folio_offset, fetch a larger length. This length may consist of
multiple contiguous pages if folio is multiorder.

Using the length calculate number of pages which will be added to bio and
increment the loop counter to skip those pages.

There is also a check to see if pages are contiguous and belong to same
folio, this is done as a COW may happen and change contiguous mapping of
pages of folio.

This technique helps to avoid overhead of merging pages which belong to
same large order folio.

Also folio-lize the functions bio_iov_add_page() and
bio_iov_add_zone_append_page()

Signed-off-by: Kundan Kumar <kundan.kumar@xxxxxxxxxxx>
---
 block/bio.c | 62 +++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 48 insertions(+), 14 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index e9e809a63c59..7857b9ca5957 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1204,7 +1204,7 @@ void bio_iov_bvec_set(struct bio *bio, struct iov_iter *iter)
 	bio_set_flag(bio, BIO_CLONED);
 }
 
-static int bio_iov_add_page(struct bio *bio, struct page *page,
+static int bio_iov_add_folio(struct bio *bio, struct folio *folio,
 		unsigned int len, unsigned int offset)
 {
 	bool same_page = false;
@@ -1214,27 +1214,27 @@ static int bio_iov_add_page(struct bio *bio, struct page *page,
 
 	if (bio->bi_vcnt > 0 &&
 	    bvec_try_merge_page(&bio->bi_io_vec[bio->bi_vcnt - 1],
-				page, len, offset, &same_page)) {
+				&folio->page, len, offset, &same_page)) {
 		bio->bi_iter.bi_size += len;
 		if (same_page)
-			bio_release_page(bio, page);
+			bio_release_page(bio, &folio->page);
 		return 0;
 	}
-	__bio_add_page(bio, page, len, offset);
+	bio_add_folio_nofail(bio, folio, len, offset);
 	return 0;
 }
 
-static int bio_iov_add_zone_append_page(struct bio *bio, struct page *page,
+static int bio_iov_add_zone_append_folio(struct bio *bio, struct folio *folio,
 		unsigned int len, unsigned int offset)
 {
 	struct request_queue *q = bdev_get_queue(bio->bi_bdev);
 	bool same_page = false;
 
-	if (bio_add_hw_page(q, bio, page, len, offset,
+	if (bio_add_hw_page(q, bio, &folio->page, len, offset,
 			queue_max_zone_append_sectors(q), &same_page) != len)
 		return -EINVAL;
 	if (same_page)
-		bio_release_page(bio, page);
+		bio_release_page(bio, &folio->page);
 	return 0;
 }
 
@@ -1258,9 +1258,9 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 	struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt;
 	struct page **pages = (struct page **)bv;
 	ssize_t size, left;
-	unsigned len, i = 0;
-	size_t offset;
-	int ret = 0;
+	unsigned int len, i = 0, j;
+	size_t offset, folio_offset;
+	int ret = 0, num_pages;
 
 	/*
 	 * Move page array up in the allocated memory for the bio vecs as far as
@@ -1301,15 +1301,49 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 
 	for (left = size, i = 0; left > 0; left -= len, i++) {
 		struct page *page = pages[i];
+		struct folio *folio = page_folio(page);
+
+		/* Calculate the offset of page in folio */
+		folio_offset = (folio_page_idx(folio, page) << PAGE_SHIFT) +
+				offset;
+
+		len = min_t(size_t, (folio_size(folio) - folio_offset), left);
+
+		num_pages = DIV_ROUND_UP(offset + len, PAGE_SIZE);
+
+		if (num_pages > 1) {
+			ssize_t bytes = left;
+			size_t contig_sz = min_t(size_t,  PAGE_SIZE - offset,
+						 bytes);
+
+			/*
+			 * Check if pages are contiguous and belong to the
+			 * same folio.
+			 */
+			for (j = i + 1; j < i + num_pages; j++) {
+				size_t next = min_t(size_t, PAGE_SIZE, bytes);
+
+				if (page_folio(pages[j]) != folio ||
+				    pages[j] != pages[j - 1] + 1) {
+					break;
+				}
+				contig_sz += next;
+				bytes -= next;
+			}
+			num_pages = j - i;
+			len = contig_sz;
+		}
 
-		len = min_t(size_t, PAGE_SIZE - offset, left);
 		if (bio_op(bio) == REQ_OP_ZONE_APPEND) {
-			ret = bio_iov_add_zone_append_page(bio, page, len,
-					offset);
+			ret = bio_iov_add_zone_append_folio(bio, folio, len,
+					folio_offset);
 			if (ret)
 				break;
 		} else
-			bio_iov_add_page(bio, page, len, offset);
+			bio_iov_add_folio(bio, folio, len, folio_offset);
+
+		/* Skip the pages which got added */
+		i = i + (num_pages - 1);
 
 		offset = 0;
 	}
-- 
2.25.1