[PATCH RFC 18/35] io_uring/zcrx: remove "struct io_copy_cache" and one nth_page() usage

David Hildenbrand
2025-08-21T21:33:43Z

We always provide a single dst page, it's unclear why the io_copy_cache
complexity is required.

So let's simplify and get rid of "struct io_copy_cache", simply working on
the single page.

... which immediately allows us for dropping one "nth_page" usage,
because it's really just a single page.

Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
io_uring/zcrx.c | 32 +++++++-------------------------
1 file changed, 7 insertions(+), 25 deletions(-)

diff --git a/io_uring/zcrx.c b/io_uring/zcrx.c
index e5ff49f3425e0..f29b2a4867516 100644
--- a/io_uring/zcrx.c
+++ b/io_uring/zcrx.c
@@ -954,29 +954,18 @@ static struct net_iov *io_zcrx_alloc_fallback(struct io_zcrx_area *area)
return niov;
}

-struct io_copy_cache {
- struct page *page;
- unsigned long offset;
- size_t size;
-};
-
-static ssize_t io_copy_page(struct io_copy_cache *cc, struct page *src_page,
+static ssize_t io_copy_page(struct page *dst_page, struct page *src_page,
unsigned int src_offset, size_t len)
{
- size_t copied = 0;
+ size_t dst_offset = 0;

- len = min(len, cc->size);
+ len = min(len, PAGE_SIZE);

while (len) {
void *src_addr, *dst_addr;
- struct page *dst_page = cc->page;
- unsigned dst_offset = cc->offset;
size_t n = len;

- 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_offset = offset_in_page(dst_offset);
+ if (folio_test_partial_kmap(page_folio(src_page))) {
src_page = nth_page(src_page, src_offset / PAGE_SIZE);
src_offset = offset_in_page(src_offset);
n = min(PAGE_SIZE - src_offset, PAGE_SIZE - dst_offset);
@@ -991,12 +980,10 @@ static ssize_t io_copy_page(struct io_copy_cache *cc, struct page *src_page,
kunmap_local(src_addr);
kunmap_local(dst_addr);

- cc->size -= n;
- cc->offset += n;
+ dst_offset += n;
len -= n;
- copied += n;
}
- return copied;
+ return dst_offset;
}

static ssize_t io_zcrx_copy_chunk(struct io_kiocb *req, struct io_zcrx_ifq *ifq,
@@ -1011,7 +998,6 @@ static ssize_t io_zcrx_copy_chunk(struct io_kiocb *req, struct io_zcrx_ifq *ifq,
return -EFAULT;

while (len) {
- struct io_copy_cache cc;
struct net_iov *niov;
size_t n;

@@ -1021,11 +1007,7 @@ static ssize_t io_zcrx_copy_chunk(struct io_kiocb *req, struct io_zcrx_ifq *ifq,
break;
}

- cc.page = io_zcrx_iov_page(niov);
- cc.offset = 0;
- cc.size = PAGE_SIZE;
-
- n = io_copy_page(&cc, src_page, src_offset, len);
+ n = io_copy_page(io_zcrx_iov_page(niov), src_page, src_offset, len);

if (!io_zcrx_queue_cqe(req, niov, ifq, 0, n)) {
io_zcrx_return_niov(niov);
--
2.50.1