linux-kernel - Re: [PATCH net-next v3] libceph: Partially revert changes to support MSG_SPLICE

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Date:   Tue, 27 Jun 2023 08:59:28 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     David Howells <dhowells@...hat.com>
Cc:     Ilya Dryomov <idryomov@...il.com>, netdev@...r.kernel.org,
        Xiubo Li <xiubli@...hat.com>, Jeff Layton <jlayton@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        Matthew Wilcox <willy@...radead.org>,
        ceph-devel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v3] libceph: Partially revert changes to
 support MSG_SPLICE_PAGES

On Tue, 27 Jun 2023 14:49:48 +0100 David Howells wrote:
> Fix the mishandling of MSG_DONTWAIT and also reinstates the per-page
> checking of the source pages (which might have come from a DIO write by
> userspace) by partially reverting the changes to support MSG_SPLICE_PAGES
> and doing things a little differently.  In messenger_v1:
> 
>  (1) The ceph_tcp_sendpage() is resurrected and the callers reverted to use
>      that.
> 
>  (2) The callers now pass MSG_MORE unconditionally.  Previously, they were
>      passing in MSG_MORE|MSG_SENDPAGE_NOTLAST and then degrading that to
>      just MSG_MORE on the last call to ->sendpage().
> 
>  (3) Make ceph_tcp_sendpage() a wrapper around sendmsg() rather than
>      sendpage(), setting MSG_SPLICE_PAGES if sendpage_ok() returns true on
>      the page.
> 
> In messenger_v2:
> 
>  (4) Bring back do_try_sendpage() and make the callers use that.
> 
>  (5) Make do_try_sendpage() use sendmsg() for both cases and set
>      MSG_SPLICE_PAGES if sendpage_ok() is set.
> 
> Fixes: 40a8c17aa770 ("ceph: Use sendmsg(MSG_SPLICE_PAGES) rather than sendpage")
> Fixes: fa094ccae1e7 ("ceph: Use sendmsg(MSG_SPLICE_PAGES) rather than sendpage()")
> Reported-by: Ilya Dryomov <idryomov@...il.com>

Ilya, would you be okay if we sent the 6.5 PR without this and then
we can either follow up with a PR in a few days or you can take this
via your tree?

Or you could review it now, that'd also work :)

In hindsight we should have pushed harder to make the FS changes as
small as possible for sendpage removal, so that they can go in via 
the appropriate tree with an appropriate level of scrutiny for 6.6,
lesson learned :(