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

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Date:	Thu, 29 Apr 2010 21:43:40 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
CC:	Lai Jiangshan <laijs@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>, kvm@...r.kernel.org
Subject: Re: [PATCH] kvm mmu: reduce 50% memory usage

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.

> @@ -393,6 +393,27 @@ static void mmu_free_rmap_desc(struct kvm_rmap_desc *rd)
>   	kfree(rd);
>   }
>
> +static gfn_t kvm_mmu_page_get_gfn(struct kvm_mmu_page *sp, int index)
> +{
> +	gfn_t gfn;
> +
> +	if (!sp->role.direct)
> +		return sp->gfns[index];
> +
> +	gfn = sp->gfn + index * (1<<  (sp->role.level - 1) * PT64_LEVEL_BITS);
> +	gfn += sp->role.quadrant<<  PT64_LEVEL_BITS;
>    

PT64_LEVEL_BITS * level

> +
> +	return gfn;
> +}
> +
>
>    


-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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