linux-kernel - Re: [PATCH v1 19/36] io_uring/zcrx: remove nth

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Message-ID: <4f366255-5dd9-44ac-878c-e44e557b8484@lucifer.local>
Date: Thu, 28 Aug 2025 17:48:56 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, Pavel Begunkov <asml.silence@...il.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, 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: Re: [PATCH v1 19/36] io_uring/zcrx: remove nth_page() usage within
 folio

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@...il.com>
> Cc: Jens Axboe <axboe@...nel.dk>
> Cc: Pavel Begunkov <asml.silence@...il.com>
> Signed-off-by: David Hildenbrand <david@...hat.com>

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

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

> ---
>  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
>