linux-kernel - Re: [PATCH] kvm mmu: reduce 50% memory usage

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Date:	Thu, 6 May 2010 16:04:02 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	Avi Kivity <avi@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
	kvm@...r.kernel.org
Subject: Re: [PATCH] kvm mmu: reduce 50% memory usage

On Thu, May 06, 2010 at 03:03:48PM +0800, Lai Jiangshan wrote:
> Marcelo Tosatti wrote:
> > On Thu, Apr 29, 2010 at 09:43:40PM +0300, Avi Kivity wrote:
> >> On 04/29/2010 09:09 PM, Marcelo Tosatti wrote:
> >>> You missed quadrant on 4mb large page emulation with shadow (see updated
> >>> patch below).
> >> Good catch.
> >>
> >>> Also for some reason i can't understand the assumption
> >>> does not hold for large sptes with TDP, so reverted for now.
> >> It's unrelated to TDP, same issue with shadow.  I think the
> >> calculation is correct.  For example the 4th spte for a level=2 page
> >> will yield gfn=4*512.
> > 
> > Under testing i see sp at level 2, with sp->gfn == 4096, mmu_set_spte
> > setting index 8 to gfn 4096 (whereas kvm_mmu_page_get_gfn returns 4096 +
> > 8*512).
> > 
> > Lai, can you please take a look at it? You should see the
> > kvm_mmu_page_set_gfn BUG_ON by using -mem-path on hugetlbfs.
> > 
> 
> Could you tell me how you test it? It will be better if I follow
> your test steps.

mount -t hugetlbfs none /mnt/
echo xyz > /proc/sys/vm/nr_hugepages
qemu-kvm parameters -mem-path /mnt/

> I also hit the kvm_mmu_page_set_gfn BUG_ON, It is because
> FNAME(fetch)() set sp->gfn wrong. The patch:
> [PATCH] kvm: calculate correct gfn for small host pages which emulates large guest pages
> fix it.
> 
> I can not hit kvm_mmu_page_set_gfn BUG_ON after this patch also
> applied.
> 
> So could you tell me your test steps:
> The host: ept/npt enabled? 64bit? testing codes in host?

Intel EPT enabled.

> The guest: OS? PAE? 32bit? 64bit? testing codes in guest?

FC12 guest.

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