On 8/22/25 14:59, David Hildenbrand wrote:

On 22.08.25 13:32, Pavel Begunkov wrote:

quoted

On 8/21/25 21:06, David Hildenbrand wrote:

quoted

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

Because it'll need to be pulled outside the loop to reuse the page for
multiple copies, i.e. packing multiple fragments of the same skb into
it. Not finished, and currently it's wasting memory.

Okay, so what you're saying is that there will be follow-up work that will actually make this structure useful.

Exactly

quoted

Why not do as below? Pages there never cross boundaries of their folios. > Do you want it to be taken into the io_uring tree?

This should better all go through the MM tree where we actually guarantee contiguous pages within a folio. (see the cover letter)

Makes sense. No objection, hopefully it won't cause too many conflicts.

quoted

diff --git a/io_uring/zcrx.c b/io_uring/zcrx.c
index e5ff49f3425e..18c12f4b56b6 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;

Yeah, I can do that in the next version given that you have plans on extending that code soon.

If we go with this version:

Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>

-- 
Pavel Begunkov