netdev - [PATCH RFC 19/35] io_uring/zcrx: remove nth

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Message-ID: <20250821200701.1329277-20-david@redhat.com>
Date: Thu, 21 Aug 2025 22:06:45 +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,
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	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
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	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>,
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	Tejun Heo <tj@...nel.org>,
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	Vlastimil Babka <vbabka@...e.cz>,
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	x86@...nel.org,
	Zi Yan <ziy@...dia.com>
Subject: [PATCH RFC 19/35] 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 src_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.

Cc: Jens Axboe <axboe@...nel.dk>
Signed-off-by: David Hildenbrand <david@...hat.com>
---
 io_uring/zcrx.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/io_uring/zcrx.c b/io_uring/zcrx.c
index f29b2a4867516..107b2a1b31c1c 100644
--- a/io_uring/zcrx.c
+++ b/io_uring/zcrx.c
@@ -966,7 +966,7 @@ static ssize_t io_copy_page(struct page *dst_page, struct page *src_page,
 		size_t n = len;
 
 		if (folio_test_partial_kmap(page_folio(src_page))) {
-			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