linux-kernel - Re: [PATCH v3 10/15] KVM: MMU: allocate shadow pages from slab

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Message-ID: <20131024095204.GD5289@redhat.com>
Date:	Thu, 24 Oct 2013 12:52:04 +0300
From:	Gleb Natapov <gleb@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Cc:	avi.kivity@...il.com, mtosatti@...hat.com, pbonzini@...hat.com,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v3 10/15] KVM: MMU: allocate shadow pages from slab

On Thu, Oct 24, 2013 at 05:29:44PM +0800, Xiao Guangrong wrote:
> On 10/24/2013 05:19 PM, Gleb Natapov wrote:
> 
> >> @@ -946,7 +947,7 @@ static inline struct kvm_mmu_page *page_header(hpa_t shadow_page)
> >>  {
> >>  	struct page *page = pfn_to_page(shadow_page >> PAGE_SHIFT);
> >>  
> >> -	return (struct kvm_mmu_page *)page_private(page);
> >> +	return (struct kvm_mmu_page *)(page->mapping);
> > Why?
> 
> That's because page->private has been used by slab:
>
But does lockless path actually looks at it?
  
> 	/* Remainder is not double word aligned */
> 	union {
> 		unsigned long private;		/* Mapping-private opaque data:
> 					 	 * usually used for buffer_heads
> 						 * if PagePrivate set; used for
> 						 * swp_entry_t if PageSwapCache;
> 						 * indicates order in the buddy
> 						 * system if PG_buddy is set.
> 						 */
> #if USE_SPLIT_PTLOCKS
> 		spinlock_t ptl;
> #endif
> 		struct kmem_cache *slab_cache;	/* SL[AU]B: Pointer to slab */
> 		struct page *first_page;	/* Compound tail pages */
> 	};

--
			Gleb.
--
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