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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Stefan Metzmacher <metze@samba.org>
Cc: Jens Axboe <axboe@kernel.dk>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Linux API Mailing List <linux-api@vger.kernel.org>,
	io-uring <io-uring@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Samba Technical <samba-technical@lists.samba.org>
Subject: Re: copy on write for splice() from file to pipe?
Date: Thu, 9 Feb 2023 11:36:02 -0800	[thread overview]
Message-ID: <CAHk-=widtNT9y-9uGMnAgyR0kzyo0XjTkExSMoGpbZgeU=+vng@mail.gmail.com> (raw)
In-Reply-To: <f6c6d42e-337a-bbab-0d36-cfcc915d26c6@samba.org>

On Thu, Feb 9, 2023 at 11:17 AM Stefan Metzmacher <metze@samba.org> wrote:
>
> Any comment about the idea of having a preadv2() flag that
> asks for a dma copy with something like async_memcpy() instead
> of the default that ends up in copy_user_enhanced_fast_string()?

I guarantee that you will only slow things down with some odd async_memcpy.

There are zero DMA engines that do memory copying better than memcpy -
the only way you can do better if is the destination isn't memory in
the first place but the final device, and then we just call it "dma".

                Linus

  reply	other threads:[~2023-02-09 19:36 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 [this message]
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
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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