netdev - Re: [PATCH v4 4/4] libceph: use sendpages_ok() instead of sendpage

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Message-ID: <6ade063f-87fa-44a2-807d-915726c2c5a9@volumez.com>
Date: Thu, 18 Jul 2024 11:31:56 +0300
From: Ofir Gal <ofir.gal@...umez.com>
To: Ilya Dryomov <idryomov@...il.com>
Cc: davem@...emloft.net, linux-block@...r.kernel.org,
 linux-nvme@...ts.infradead.org, netdev@...r.kernel.org,
 ceph-devel@...r.kernel.org, dhowells@...hat.com, edumazet@...gle.com,
 pabeni@...hat.com, kbusch@...nel.org, xiubli@...hat.com
Subject: Re: [PATCH v4 4/4] libceph: use sendpages_ok() instead of
 sendpage_ok()


On 7/17/24 23:26, Ilya Dryomov wrote:
> On Tue, Jul 16, 2024 at 2:46 PM Ofir Gal <ofir.gal@...umez.com> wrote:
>>
>> Xiubo/Ilya please take a look
>>
>> On 6/11/24 09:36, Ofir Gal wrote:
>>> Currently ceph_tcp_sendpage() and do_try_sendpage() use sendpage_ok() in
>>> order to enable MSG_SPLICE_PAGES, it check the first page of the
>>> iterator, the iterator may represent contiguous pages.
>>>
>>> MSG_SPLICE_PAGES enables skb_splice_from_iter() which checks all the
>>> pages it sends with sendpage_ok().
>>>
>>> When ceph_tcp_sendpage() or do_try_sendpage() send an iterator that the
>>> first page is sendable, but one of the other pages isn't
>>> skb_splice_from_iter() warns and aborts the data transfer.
>>>
>>> Using the new helper sendpages_ok() in order to enable MSG_SPLICE_PAGES
>>> solves the issue.
>>>
>>> Signed-off-by: Ofir Gal <ofir.gal@...umez.com>
>>> ---
>>>  net/ceph/messenger_v1.c | 2 +-
>>>  net/ceph/messenger_v2.c | 2 +-
>>>  2 files changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/net/ceph/messenger_v1.c b/net/ceph/messenger_v1.c
>>> index 0cb61c76b9b8..a6788f284cd7 100644
>>> --- a/net/ceph/messenger_v1.c
>>> +++ b/net/ceph/messenger_v1.c
>>> @@ -94,7 +94,7 @@ static int ceph_tcp_sendpage(struct socket *sock, struct page *page,
>>>        * coalescing neighboring slab objects into a single frag which
>>>        * triggers one of hardened usercopy checks.
>>>        */
>>> -     if (sendpage_ok(page))
>>> +     if (sendpages_ok(page, size, offset))
>>>               msg.msg_flags |= MSG_SPLICE_PAGES;
>>>
>>>       bvec_set_page(&bvec, page, size, offset);
>>> diff --git a/net/ceph/messenger_v2.c b/net/ceph/messenger_v2.c
>>> index bd608ffa0627..27f8f6c8eb60 100644
>>> --- a/net/ceph/messenger_v2.c
>>> +++ b/net/ceph/messenger_v2.c
>>> @@ -165,7 +165,7 @@ static int do_try_sendpage(struct socket *sock, struct iov_iter *it)
>>>                * coalescing neighboring slab objects into a single frag
>>>                * which triggers one of hardened usercopy checks.
>>>                */
>>> -             if (sendpage_ok(bv.bv_page))
>>> +             if (sendpages_ok(bv.bv_page, bv.bv_len, bv.bv_offset))
>>>                       msg.msg_flags |= MSG_SPLICE_PAGES;
>>>               else
>>>                       msg.msg_flags &= ~MSG_SPLICE_PAGES;
>>
>
> Hi Ofir,
>
> Ceph should be fine as is -- there is an internal "cursor" abstraction
> that that is limited to PAGE_SIZE chunks, using bvec_iter_bvec() instead
> of mp_bvec_iter_bvec(), etc.  This means that both do_try_sendpage() and
> ceph_tcp_sendpage() should be called only with
>
>   page_off + len <= PAGE_SIZE
>
> being true even if the page is contiguous (and that we lose out on the
> potential performance benefit, of course...).
>
> That said, if the plan is to remove sendpage_ok() so that it doesn't
> accidentally grow new users who are unaware of this pitfall, consider
> this
>
> Acked-by: Ilya Dryomov <idryomov@...il.com>
>
> Thanks,
>
>                 Ilya
I dont think the plan is to remove sendpage_ok() (unless someone says
otherwise). Im sending v5 without the libceph patch.

Thanks