On 03/20/2012 12:48 PM, Peter Zijlstra wrote: > On Tue, 2012-03-20 at 12:18 +0200, Avi Kivity wrote: > > 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. > > But wouldn't you then have to wait for the entire copy to complete > before accessing any of the memory? That sounds like a way worse latency > hit than the per-page lazy-migrate. You use the dma engine for eager copying, not on demand. -- error compiling committee.c: too many arguments to function -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>