From: Jens Axboe <[email protected]>
To: Andy Lutomirski <[email protected]>
Cc: Linus Torvalds <[email protected]>,
Dave Chinner <[email protected]>,
Matthew Wilcox <[email protected]>,
Stefan Metzmacher <[email protected]>,
linux-fsdevel <[email protected]>,
Linux API Mailing List <[email protected]>,
io-uring <[email protected]>,
"[email protected]" <[email protected]>,
Al Viro <[email protected]>,
Samba Technical <[email protected]>
Subject: Re: copy on write for splice() from file to pipe?
Date: Fri, 10 Feb 2023 14:51:52 -0700 [thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
On 2/10/23 2:27 PM, Jens Axboe wrote:
> On 2/10/23 2:14?PM, Andy Lutomirski wrote:
>> On Fri, Feb 10, 2023 at 12:50 PM Jens Axboe <[email protected]> wrote:
>>>
>>> On 2/10/23 1:44?PM, Linus Torvalds wrote:
>>>> On Fri, Feb 10, 2023 at 12:39 PM Jens Axboe <[email protected]> wrote:
>>>>>
>>>>> Right, I'm referencing doing zerocopy data sends with io_uring, using
>>>>> IORING_OP_SEND_ZC. This isn't from a file, it's from a memory location,
>>>>> but the important bit here is the split notifications and how you
>>>>> could wire up a OP_SENDFILE similarly to what Andy described.
>>>>
>>>> Sure, I think it's much more reasonable with io_uring than with splice itself.
>>>>
>>>> So I was mainly just reacting to the "strict-splice" thing where Andy
>>>> was talking about tracking the page refcounts. I don't think anything
>>>> like that can be done at a splice() level, but higher levels that
>>>> actually know about the whole IO might be able to do something like
>>>> that.
>>>>
>>>> Maybe we're just talking past each other.
>>>
>>> Maybe slightly, as I was not really intending to comment on the strict
>>> splice thing. But yeah I agree on splice, it would not be trivial to do
>>> there. At least with io_uring we have the communication channel we need.
>>> And tracking page refcounts seems iffy and fraught with potential
>>> issues.
>>>
>>
>> Hmm.
>>
>> Are there any real-world use cases for zero-copy splice() that
>> actually depend on splicing from a file to a pipe and then later from
>> the pipe to a socket (or file or whatever)? Or would everything
>> important be covered by a potential new io_uring operation that copies
>> from one fd directly to another fd?
>
> I think it makes sense. As Linus has referenced, the sex appeal of
> splice is the fact that it is dealing with pipes, and you can access
> these internal buffers through other means. But that is probably largely
> just something that is sexy design wise, nothing that _really_ matters
> in practice. And the pipes do get in the way, for example I had to add
> pipe resizing fcntl helpers to bump the size. If you're doing a plain
> sendfile, the pipes just kind of get in the way too imho.
>
> Another upside (from the io_uring) perspective is that splice isn't very
> efficient through io_uring, as it requires offload to io-wq. This could
> obviously be solved by some refactoring in terms of non-blocking, but it
> hasn't really been that relevant (and nobody has complained about it). A
> new sendfile op would nicely get around that too as it could be designed
> with async in nature, rather than the classic sync syscall model that
> splice follows.
Speaking of splice/io_uring, Ming posted this today:
https://lore.kernel.org/io-uring/[email protected]/
--
Jens Axboe
next prev parent reply other threads:[~2023-02-10 21:52 UTC|newest]
Thread overview: 64+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-09 13:55 copy on write for splice() from file to pipe? Stefan Metzmacher
2023-02-09 14:11 ` Matthew Wilcox
2023-02-09 14:29 ` Stefan Metzmacher
2023-02-09 16:41 ` Linus Torvalds
2023-02-09 19:17 ` Stefan Metzmacher
2023-02-09 19:36 ` Linus Torvalds
2023-02-09 19:48 ` Linus Torvalds
2023-02-09 20:33 ` Jeremy Allison
2023-02-10 20:45 ` Stefan Metzmacher
2023-02-10 20:51 ` Linus Torvalds
2023-02-10 2:16 ` Dave Chinner
2023-02-10 4:06 ` Dave Chinner
2023-02-10 4:44 ` Matthew Wilcox
2023-02-10 6:57 ` Dave Chinner
2023-02-10 15:14 ` Andy Lutomirski
2023-02-10 16:33 ` Linus Torvalds
2023-02-10 17:57 ` Andy Lutomirski
2023-02-10 18:19 ` Jeremy Allison
2023-02-10 19:29 ` Stefan Metzmacher
2023-02-10 18:37 ` Linus Torvalds
2023-02-10 19:01 ` Andy Lutomirski
2023-02-10 19:18 ` Linus Torvalds
2023-02-10 19:27 ` Jeremy Allison
2023-02-10 19:42 ` Stefan Metzmacher
2023-02-10 19:42 ` Linus Torvalds
2023-02-10 19:54 ` Stefan Metzmacher
2023-02-10 19:29 ` Linus Torvalds
2023-02-13 9:07 ` Herbert Xu
2023-02-10 19:55 ` Andy Lutomirski
2023-02-10 20:27 ` Linus Torvalds
2023-02-10 20:32 ` Jens Axboe
2023-02-10 20:36 ` Linus Torvalds
2023-02-10 20:39 ` Jens Axboe
2023-02-10 20:44 ` Linus Torvalds
2023-02-10 20:50 ` Jens Axboe
2023-02-10 21:14 ` Andy Lutomirski
2023-02-10 21:27 ` Jens Axboe
2023-02-10 21:51 ` Jens Axboe [this message]
2023-02-10 22:08 ` Linus Torvalds
2023-02-10 22:16 ` Jens Axboe
2023-02-10 22:17 ` Linus Torvalds
2023-02-10 22:25 ` Jens Axboe
2023-02-10 22:35 ` Linus Torvalds
2023-02-10 22:51 ` Jens Axboe
2023-02-11 3:18 ` Ming Lei
2023-02-11 6:17 ` Ming Lei
2023-02-11 14:13 ` Jens Axboe
2023-02-11 15:05 ` Ming Lei
2023-02-11 15:33 ` Jens Axboe
2023-02-11 18:57 ` Linus Torvalds
2023-02-12 2:46 ` Jens Axboe
2023-02-10 4:47 ` Linus Torvalds
2023-02-10 6:19 ` Dave Chinner
2023-02-10 17:23 ` Linus Torvalds
2023-02-10 17:47 ` Linus Torvalds
2023-02-13 9:28 ` Herbert Xu
2023-02-10 22:41 ` David Laight
2023-02-10 22:51 ` Jens Axboe
2023-02-13 9:30 ` Herbert Xu
2023-02-13 9:25 ` Herbert Xu
2023-02-13 18:01 ` Andy Lutomirski
2023-02-14 1:22 ` Herbert Xu
2023-02-17 23:13 ` Andy Lutomirski
2023-02-20 4:54 ` Herbert Xu
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