[PATCH] block: add larger order folio instead of pages for passthrough I/O

[Chinmay Gameti <c.gameti@xxxxxxxxxxx>]

This patch supports adding a large folio to bio for passthrough I/Os,
when mTHP is enabled. Similar to block I/O folio changes [1].

These changes reduce the overhead incurred by bio_map_user_iov for
passthrough I/O.

Perf diff before and after this change:

perf diff for write I/O with 64K block size:
        0.84%   -0.49%  [kernel.kallsyms]       [k] bio_map_user_iov
        1.23%           [kernel.kallsyms]       [k] bvec_try_merge_page
        0.88%           [kernel.kallsyms]       [k] bvec_try_merge_hw_page
perf diff for read I/O with 64K block size:
        1.74%   -1.1%   [kernel.kallsyms]       [k] bio_map_user_iov
        2.39%           [kernel.kallsyms]       [k] bvec_try_merge_page
        1.74%           [kernel.kallsyms]       [k] bvec_try_merge_hw_page

perf diff for write I/O with 128K block size:
        0.84%   -0.6%   [kernel.kallsyms]       [k] bio_map_user_iov
        1.49%           [kernel.kallsyms]       [k] bvec_try_merge_page
        1.19%           [kernel.kallsyms]       [k] bvec_try_merge_hw_page
perf diff for read I/O with 128K block size:
        2.35%   -1.56%  [kernel.kallsyms]       [k] bio_map_user_iov
        4.53%           [kernel.kallsyms]       [k] bvec_try_merge_page
        3.39%           [kernel.kallsyms]       [k] bvec_try_merge_hw_page

[1] commit ed9832bc08db ("block: introduce folio awareness and add a
bigger size from folio")

Signed-off-by: Chinmay Gameti <c.gameti@xxxxxxxxxxx>
Signed-off-by: Kundan Kumar <kundan.kumar@xxxxxxxxxxx>
---
 block/bio.c         |  8 ++++----
 block/blk-map.c     | 31 +++++++++++++++++++++++--------
 include/linux/bio.h |  4 ++++
 3 files changed, 31 insertions(+), 12 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 699a78c85c75..50e8b565f368 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1203,10 +1203,10 @@ static int bio_iov_add_folio(struct bio *bio, struct folio *folio, size_t len,
 	return 0;
 }
 
-static unsigned int get_contig_folio_len(unsigned int *num_pages,
-					 struct page **pages, unsigned int i,
-					 struct folio *folio, size_t left,
-					 size_t offset)
+unsigned int get_contig_folio_len(unsigned int *num_pages,
+				  struct page **pages, unsigned int i,
+				  struct folio *folio, size_t left,
+				  size_t offset)
 {
 	size_t bytes = left;
 	size_t contig_sz = min_t(size_t, PAGE_SIZE - offset, bytes);
diff --git a/block/blk-map.c b/block/blk-map.c
index b5fd1d857461..216d08c8b0de 100644
--- a/block/blk-map.c
+++ b/block/blk-map.c
@@ -295,8 +295,9 @@ static int bio_map_user_iov(struct request *rq, struct iov_iter *iter,
 		struct page *stack_pages[UIO_FASTIOV];
 		struct page **pages = stack_pages;
 		ssize_t bytes;
-		size_t offs;
 		int npages;
+		unsigned int num_pages;
+		size_t offs, folio_offset, len;
 
 		if (nr_vecs > ARRAY_SIZE(stack_pages))
 			pages = NULL;
@@ -313,21 +314,35 @@ static int bio_map_user_iov(struct request *rq, struct iov_iter *iter,
 		if (unlikely(offs & queue_dma_alignment(rq->q)))
 			j = 0;
 		else {
-			for (j = 0; j < npages; j++) {
+			for (j = 0; j < npages; j += num_pages) {
 				struct page *page = pages[j];
-				unsigned int n = PAGE_SIZE - offs;
+				struct folio *folio = page_folio(page);
 				bool same_page = false;
 
-				if (n > bytes)
-					n = bytes;
 
-				if (!bio_add_hw_page(rq->q, bio, page, n, offs,
-						     max_sectors, &same_page))
+				folio_offset = ((size_t)folio_page_idx(folio,
+						page) << PAGE_SHIFT) + offs;
+
+				len = min(folio_size(folio) - folio_offset,
+					  (size_t)bytes);
+
+				num_pages = DIV_ROUND_UP(offs + len,
+							 PAGE_SIZE);
+
+				if (num_pages > 1)
+					len = get_contig_folio_len(
+							&num_pages, pages, j,
+							folio, (size_t)bytes,
+							offs);
+
+				if (!bio_add_hw_folio(rq->q, bio, folio, len,
+						      folio_offset, max_sectors,
+						      &same_page))
 					break;
 
 				if (same_page)
 					bio_release_page(bio, page);
-				bytes -= n;
+				bytes -= len;
 				offs = 0;
 			}
 		}
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 60830a6a5939..1e5fbc875ecc 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -422,6 +422,10 @@ void __bio_add_page(struct bio *bio, struct page *page,
 		unsigned int len, unsigned int off);
 void bio_add_folio_nofail(struct bio *bio, struct folio *folio, size_t len,
 			  size_t off);
+unsigned int get_contig_folio_len(unsigned int *num_pages,
+				  struct page **pages, unsigned int i,
+				  struct folio *folio, size_t left,
+				  size_t offset);
 int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter);
 void bio_iov_bvec_set(struct bio *bio, struct iov_iter *iter);
 void __bio_release_pages(struct bio *bio, bool mark_dirty);
-- 
2.34.1