[PATCH v5 2/3] block: add folio awareness instead of looping through pages

[Kundan Kumar <kundan.kumar@samsung.com>]

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.

Using a helper function check 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@samsung.com>
---
 block/bio.c | 72 ++++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 58 insertions(+), 14 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index c8914febb16e..3e75b5b0eb6e 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1224,7 +1224,7 @@ 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;
@@ -1234,30 +1234,60 @@ 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(folio, 0), len, offset,
+                               &same_page)) {
                bio->bi_iter.bi_size += len;
                if (same_page)
-                       bio_release_page(bio, page);
+                       bio_release_page(bio, folio_page(folio, 0));
                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_folio(q, bio, folio, 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(folio, 0));
        return 0;
 }

+static unsigned int get_contig_folio_len(int *num_pages, struct page **pages,
+                                        int i, struct folio *folio,
+                                        ssize_t left, size_t offset)
+{
+       ssize_t bytes = left;
+       size_t contig_sz = min_t(size_t,  PAGE_SIZE - offset, bytes);
+       unsigned int j;
+
+       /*
+        * We might COW a single page in the middle of
+        * a large folio, so we have to check that all
+        * pages belong to the same folio.
+        */
+       bytes -= contig_sz;
+       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;
+
+       return contig_sz;
+}
+
 #define PAGE_PTRS_PER_BVEC     (sizeof(struct bio_vec) / sizeof(struct page *))

 /**
@@ -1277,9 +1307,9 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
        unsigned short entries_left = bio->bi_max_vecs - bio->bi_vcnt;
        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;
+       ssize_t size, left, len;
+       unsigned int i = 0, num_pages;
+       size_t offset, folio_offset;
        int ret = 0;

        /*
@@ -1321,15 +1351,29 @@ 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);
+
+               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)
+                       len = get_contig_folio_len(&num_pages, pages, i,
+                                                  folio, left, offset);

-               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