linux-kernel - Re: [PATCH net-next v2 10/17] nvme: Use sendmsg(MSG_SPLICE

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Date:   Tue, 20 Jun 2023 16:00:31 +0300
From:   Sagi Grimberg <sagi@...mberg.me>
To:     David Howells <dhowells@...hat.com>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     netdev@...r.kernel.org,
        Alexander Duyck <alexander.duyck@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        David Ahern <dsahern@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Jens Axboe <axboe@...nel.dk>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Keith Busch <kbusch@...nel.org>,
        Jens Axboe <axboe@...com>, Christoph Hellwig <hch@....de>,
        Chaitanya Kulkarni <kch@...dia.com>,
        linux-nvme@...ts.infradead.org
Subject: Re: [PATCH net-next v2 10/17] nvme: Use sendmsg(MSG_SPLICE_PAGES)
 rather then sendpage


>>>      struct bio_vec bvec;
>>>      struct msghdr msg = { .msg_flags = MSG_SPLICE_PAGES | ... };
>>>
>>>      ..
>>>
>>>      bvec_set_virt
>>>      iov_iter_bvec
>>>      sock_sendmsg
>>>
>>> is a frequent pattern. Does it make sense to define a wrapper? Same 
>>> for bvec_set_page.
>>
>> I dunno.  I'm trying to move towards aggregating multiple pages in a bvec
>> before calling sendmsg if possible rather than doing it one page at a 
>> time,
>> but it's easier and more obvious in some places than others.
> 
> That would be great to do, but nvme needs to calculate a data digest
> and doing that in a separate scan of the payload is not very cache
> friendly...
> 
> There is also the fact that the payload may be sent in portions 
> asynchronously driven by how the controller wants to accept them,
> so there is some complexity there.
> 
> But worth looking at for sure.
> 
> The patch looks good to me, taking it to run some tests
> (from sendpage-3-frag branch in your kernel.org tree correct?)
> 
> For now, you can add:
> Reviewed-by: Sagi Grimberg <sagi@...mberg.me>

Patches seem to hold up.
Tested-by: Sagi Grimberg <sagi@...mberg.me>

However if possible, can you please split nvme/host and nvme/target
changes? We try to separate host side and target side changes in the
same patch.