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

From: Shirley Ma
Date: Mon Aug 02 2010 - 12:02:48 EST

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). So get_user_pages_fast will
call slow path get_user_pages.

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


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