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Date: Mon, 02 Aug 2010 19:32:24 +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 07:25 PM, Shirley Ma wrote: > On Mon, 2010-08-02 at 19:11 +0300, Avi Kivity wrote: >> I don't understand this. gup_fast() only calls gup() if the page is >> swapped out or read-only. > Oh, I used the page as read-only on xmit path. Should I use write > instead? No, for xmit getting the page as read only is fine. I was inaccurate, gup_fast() performs as follows: - if .write = 1, gup_fast() will be fast if the page is mapped and writeable - if .write = 0, gup_fast() will be fast if the page is mapped so, using .write = 0 for the xmit path will be faster in more cases than .write = 1. When are you seeing gup_fast() fall back to gup()? It should be at most once per page (when a guest starts up none of its pages are mapped, it faults them in on demand). -- error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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