[PATCH v1 19/36] io_uring/zcrx: remove nth_page() usage within folio

Within a folio/compound page, nth_page() is no longer required.
Given that we call folio_test_partial_kmap()+kmap_local_page(), the code
would already be problematic if the pages would span multiple folios.

So let's just assume that all src pages belong to a single
folio/compound page and can be iterated ordinarily. The dst page is
currently always a single page, so we're not actually iterating
anything.

Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: David Hildenbrand <redacted>
---
 io_uring/zcrx.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/io_uring/zcrx.c b/io_uring/zcrx.c
index e5ff49f3425e0..18c12f4b56b6c 100644
--- a/io_uring/zcrx.c
+++ b/io_uring/zcrx.c

@@ -975,9 +975,9 @@ static ssize_t io_copy_page(struct io_copy_cache *cc, struct page *src_page,
 
 		if (folio_test_partial_kmap(page_folio(dst_page)) ||
 		    folio_test_partial_kmap(page_folio(src_page))) {
-			dst_page = nth_page(dst_page, dst_offset / PAGE_SIZE);
+			dst_page += dst_offset / PAGE_SIZE;
 			dst_offset = offset_in_page(dst_offset);
-			src_page = nth_page(src_page, src_offset / PAGE_SIZE);
+			src_page += src_offset / PAGE_SIZE;
 			src_offset = offset_in_page(src_offset);
 			n = min(PAGE_SIZE - src_offset, PAGE_SIZE - dst_offset);
 			n = min(n, len);

-- 
2.50.1

On Thu, Aug 28, 2025 at 12:01:23AM +0200, David Hildenbrand wrote:

Within a folio/compound page, nth_page() is no longer required.
Given that we call folio_test_partial_kmap()+kmap_local_page(), the code
would already be problematic if the pages would span multiple folios.

So let's just assume that all src pages belong to a single
folio/compound page and can be iterated ordinarily. The dst page is
currently always a single page, so we're not actually iterating
anything.

Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: David Hildenbrand <redacted>

On basis of src pages being within the same folio, LGTM, so:

Reviewed-by: Lorenzo Stoakes <redacted>