netdev - [PATCH v7 02/23] iov_iter: DDP copy to iter/pages

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Date:   Tue, 25 Oct 2022 16:59:37 +0300
From:   Aurelien Aptel <aaptel@...dia.com>
To:     netdev@...r.kernel.org, davem@...emloft.net, kuba@...nel.org,
        edumazet@...gle.com, pabeni@...hat.com, saeedm@...dia.com,
        tariqt@...dia.com, leon@...nel.org, linux-nvme@...ts.infradead.org,
        sagi@...mberg.me, hch@....de, kbusch@...nel.org, axboe@...com,
        chaitanyak@...dia.com
Cc:     smalin@...dia.com, aaptel@...dia.com, ogerlitz@...dia.com,
        yorayz@...dia.com, borisp@...dia.com, aurelien.aptel@...il.com,
        malin1024@...il.com
Subject: [PATCH v7 02/23] iov_iter: DDP copy to iter/pages

From: Ben Ben-Ishay <benishay@...dia.com>

When using direct data placement (DDP) the NIC writes some of the payload
directly to the destination buffer, and constructs SKBs such that they
point to this data. To skip copies when SKB data already resides in the
destination we use the newly introduced routines in this commit, which
check if (src == dst), and skip the copy when that's true.

As the current user for these routines is in the block layer (nvme-tcp),
then we only apply the change for bio_vec. Other routines use the normal
methods for copying.

Signed-off-by: Ben Ben-Ishay <benishay@...dia.com>
Signed-off-by: Boris Pismenny <borisp@...dia.com>
Signed-off-by: Or Gerlitz <ogerlitz@...dia.com>
Signed-off-by: Yoray Zack <yorayz@...dia.com>
Signed-off-by: Shai Malin <smalin@...dia.com>
Signed-off-by: Aurelien Aptel <aaptel@...dia.com>
Reviewed-by: Chaitanya Kulkarni <kch@...dia.com>
---
 lib/iov_iter.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index c3ca28ca68a6..75470a4b8ab3 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -526,7 +526,7 @@ size_t _copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
 		might_fault();
 	iterate_and_advance(i, bytes, base, len, off,
 		copyout(base, addr + off, len),
-		memcpy(base, addr + off, len)
+		(base != addr + off) && memcpy(base, addr + off, len)
 	)
 
 	return bytes;
-- 
2.31.1