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

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Message-ID: <4BE269D4.9090108@cn.fujitsu.com>
Date:	Thu, 06 May 2010 15:03:48 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Marcelo Tosatti <mtosatti@...hat.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

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.

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

Lai
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