netdev - Re: [RFC PATCH v8 00/16] Provide a zero-copy method on KVM virtio-net.

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Message-ID: <4C56EE3D.1050203@redhat.com>
Date:	Mon, 02 Aug 2010 19:11:41 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Shirley Ma <mashirle@...ibm.com>
CC:	xiaohui.xin@...el.com, netdev@...r.kernel.org, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, mst@...hat.com, mingo@...e.hu,
	davem@...emloft.net, herbert@...dor.hengli.com.au,
	jdike@...ux.intel.com
Subject: Re: [RFC PATCH v8 00/16] Provide a zero-copy method on KVM virtio-net.

  On 08/02/2010 07:01 PM, Shirley Ma wrote:
> Hello Avi,
>
> On Sun, 2010-08-01 at 11:18 +0300, Avi Kivity wrote:
>> I don't understand.  Under what conditions do you use
>> get_user_pages()
>> instead of get_user_pages_fast()?  Why?
> The code always calls get_user_pages_fast, however, the page will be
> unpinned in skb_free if the same page is not used again for a new
> buffer. The reason for unpin the page is we don't want to pin all of the
> guest kernel memory(memory over commit).

That is fine.

> So get_user_pages_fast will
> call slow path get_user_pages.

I don't understand this. gup_fast() only calls gup() if the page is 
swapped out or read-only.

> Your previous comment is suggesting to keep the page pinned for
> get_user_pages_fast fast path?
>

Right now I'm not sure I understand what's happening.

-- 
error compiling committee.c: too many arguments to function

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