linux-kernel - Re: [PATCH 3/3] kvm mmu: alloc shadow pages with __GFP

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Date:	Wed, 18 Feb 2009 13:47:04 +0000
From:	Avi Kivity <avi@...hat.com>
To:	Joerg Roedel <joerg.roedel@....com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] kvm mmu: alloc shadow pages with __GFP_ZERO

Joerg Roedel wrote:
> Not using __GFP_ZERO when allocating shadow pages triggers the
> assertion in the kvm_mmu_alloc_page() when MMU debugging is enabled.
>
> Signed-off-by: Joerg Roedel <joerg.roedel@....com>
> ---
>  arch/x86/kvm/mmu.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index c90b4b2..d93ecec 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -301,7 +301,7 @@ static int mmu_topup_memory_cache_page(struct kvm_mmu_memory_cache *cache,
>  	if (cache->nobjs >= min)
>  		return 0;
>  	while (cache->nobjs < ARRAY_SIZE(cache->objects)) {
> -		page = alloc_page(GFP_KERNEL);
> +		page = alloc_page(GFP_KERNEL | __GFP_ZERO);
>  		if (!page)
>  			return -ENOMEM;
>  		set_page_private(page, 0);
>   

What is the warning?

Adding __GFP_ZERO here will cause us to clear the page twice, which is 
wasteful.


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

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