From: "Patrick J. LoPresti" <lopresti@gmail.com>
To: Bryan Donlan <bdonlan@gmail.com>
Cc: linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: sendfile() expert advice sought
Date: Wed, 17 Feb 2010 18:47:07 -0800 [thread overview]
Message-ID: <23986fd91002171847l749e71eh6a71259b1ff0a2df@mail.gmail.com> (raw)
In-Reply-To: <3e8340491002171819h4d63d592ube70f327eb92d798@mail.gmail.com>
On Wed, Feb 17, 2010 at 6:19 PM, Bryan Donlan <bdonlan@gmail.com> wrote:
>
> sendfile() always copies pages
Really? So the description in the following article (see "Figure 4") is wrong?
http://www.linuxjournal.com/article/6345?page=0,1
(To be clear, I want to replace the step where the kernel buffers get
populated from disk with a step where I populate them programatically.
That is what I mean by "sendfile() for anonymous pages".)
According to that article, among others, if your network device
supports scatter/gather and the pages are already resident, then
sendfile() is a true zero-copy operation. That is, it takes page
cache pages and arranges to DMA them to the network card without
creating any additional copies in system RAM.
My questions make a lot more sense if that is how it works, anyway :-).
- Pat
prev parent reply other threads:[~2010-02-18 2:47 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-02-16 19:53 sendfile() expert advice sought Patrick J. LoPresti
2010-02-18 0:57 ` Robert Hancock
2010-02-18 2:19 ` Bryan Donlan
2010-02-18 2:47 ` Patrick J. LoPresti [this message]
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