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Date: Tue, 20 Mar 2012 12:18:08 +0200
From: Avi Kivity <avi@redhat.com>
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To: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
        Paul Turner <pjt@google.com>,
        Suresh Siddha <suresh.b.siddha@intel.com>,
        Mike Galbraith <efault@gmx.de>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Lai Jiangshan <laijs@cn.fujitsu.com>, Dan Smith <danms@us.ibm.com>,
        Bharata B Rao <bharata.rao@gmail.com>,
        Lee Schermerhorn <Lee.Schermerhorn@hp.com>,
        Andrea Arcangeli <aarcange@redhat.com>, Rik van Riel <riel@redhat.com>,
        Johannes Weiner <hannes@cmpxchg.org>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [RFC][PATCH 00/26] sched/numa
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On 03/19/2012 10:03 PM, Peter Zijlstra wrote:
> On Mon, 2012-03-19 at 14:16 +0200, Avi Kivity wrote:
> > > Afaik we do not use dma engines for memory migration. 
> > 
> > We don't, but I think we should. 
>
> ISTR we (the community) had this discussion once. I also seem to
> remember the general consensus being that DMA engines would mostly
> likely not be worth the effort, although I can't really recall the
> specifics.
>
> Esp. for 4k pages the setup of the offload will likely be more expensive
> than actually doing the memcpy.

If you're copying a page, yes.  If you're copying a large vma, the
per-page setup cost is likely to be very low.

Especially if you're copying across nodes.

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