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

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Date:   Tue, 27 Jun 2023 18:08:19 +0200
From:   Ilya Dryomov <idryomov@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     David Howells <dhowells@...hat.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, Jun 27, 2023 at 5:59 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> 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 :(

Hi Jakub,

This patch looks good to me.  I have been meaning to actually test
it, but, if time is of the essence, I'm OK with it being merged via
the networking tree now.

Reviewed-by: Ilya Dryomov <idryomov@...il.com>

Thanks,

                Ilya