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

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Message-ID: <5268E888.7060608@linux.vnet.ibm.com>
Date:	Thu, 24 Oct 2013 17:29:44 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
To:	Gleb Natapov <gleb@...hat.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 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:

	/* 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 */
	};

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