* Avi Kivity <avi@xxxxxxxxxx> wrote: > On 05/30/2011 05:10 PM, Ingo Molnar wrote: > >> [...] Windows has a zeroing thread which causes all of RAM to be > >> committed shortly after boot, though. > > > > heh, maybe they read lkml and copied my ancient idea: > > > > http://people.redhat.com/mingo/clearpage-patches/clearpage-2.3.18-J1 > > > > An earlier version had a 'zerod' (page zeroing kernel thread). > > > > This was one of my more stupid ideas btw. > > > > I think that with a dma engine it makes sense. We've got an extra > resource, why not utilize it in the background? Some workloads > generate a lot of demand for zero pages. It was one of the early ideas to use DMA engines to clear memory slowly in the background. > I agree that using the cpu to clear memory is not a good idea, it > just causes cache pollution. Yeah, but even cache-neutral clearing (either driven from the CPU from the idle thread or by a DMA engine) is not a particularly good idea: because it uses up a finite resource: memory bandwidth. Can we create 'idle' DMA transactions - once that never get in the way of real DMA transactions? Also, a profile of a typical kernel build shows: 0.69% cc1 [kernel.kallsyms] [k] clear_page_c 0.49% cc1 [kernel.kallsyms] [k] page_fault So while we could improve it, the question is, can we do this without accidentally slowing things down by more than 0.69%? And kernel builds are a pretty clear_page_c() intense workload. Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
