linux-kernel - [PATCH RFC 18/35] io_uring/zcrx: remove "struct io_copy_cache" and one nth

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Message-ID: <20250821200701.1329277-19-david@redhat.com>
Date: Thu, 21 Aug 2025 22:06:44 +0200
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: David Hildenbrand <david@...hat.com>,
	Jens Axboe <axboe@...nel.dk>,
	Alexander Potapenko <glider@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Brendan Jackman <jackmanb@...gle.com>,
	Christoph Lameter <cl@...two.org>,
	Dennis Zhou <dennis@...nel.org>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	dri-devel@...ts.freedesktop.org,
	intel-gfx@...ts.freedesktop.org,
	iommu@...ts.linux.dev,
	io-uring@...r.kernel.org,
	Jason Gunthorpe <jgg@...dia.com>,
	Johannes Weiner <hannes@...xchg.org>,
	John Hubbard <jhubbard@...dia.com>,
	kasan-dev@...glegroups.com,
	kvm@...r.kernel.org,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-arm-kernel@...s.com,
	linux-arm-kernel@...ts.infradead.org,
	linux-crypto@...r.kernel.org,
	linux-ide@...r.kernel.org,
	linux-kselftest@...r.kernel.org,
	linux-mips@...r.kernel.org,
	linux-mmc@...r.kernel.org,
	linux-mm@...ck.org,
	linux-riscv@...ts.infradead.org,
	linux-s390@...r.kernel.org,
	linux-scsi@...r.kernel.org,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Marco Elver <elver@...gle.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Michal Hocko <mhocko@...e.com>,
	Mike Rapoport <rppt@...nel.org>,
	Muchun Song <muchun.song@...ux.dev>,
	netdev@...r.kernel.org,
	Oscar Salvador <osalvador@...e.de>,
	Peter Xu <peterx@...hat.com>,
	Robin Murphy <robin.murphy@....com>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Tejun Heo <tj@...nel.org>,
	virtualization@...ts.linux.dev,
	Vlastimil Babka <vbabka@...e.cz>,
	wireguard@...ts.zx2c4.com,
	x86@...nel.org,
	Zi Yan <ziy@...dia.com>
Subject: [PATCH RFC 18/35] io_uring/zcrx: remove "struct io_copy_cache" and one nth_page() usage

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@...nel.dk>
Signed-off-by: David Hildenbrand <david@...hat.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