linux-kernel - Re: [PATCH 5/6] KVM MMU: reduce kvm_mmu

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Message-ID: <4BC2DB95.70704@redhat.com>
Date:	Mon, 12 Apr 2010 11:36:37 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	KVM list <kvm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/6] KVM MMU: reduce kvm_mmu_page size

On 04/12/2010 11:05 AM, Xiao Guangrong wrote:
> 'multimapped' and 'unsync' in 'struct kvm_mmu_page' are just indication
> field, we can use flag bits instand of them
>
> @@ -202,9 +202,10 @@ struct kvm_mmu_page {
>   	 * in this shadow page.
>   	 */
>   	DECLARE_BITMAP(slot_bitmap, KVM_MEMORY_SLOTS + KVM_PRIVATE_MEM_SLOTS);
> -	int multimapped;         /* More than one parent_pte? */
>   	int root_count;          /* Currently serving as active root */
> -	bool unsync;
> +	#define MMU_PAGE_MULTIMAPPED 0x1        /* More than one parent_pte? */
> +	#define MMU_PAGE_UNSYNC 0x2
> +	unsigned int flags;
>   	unsigned int unsync_children;
>   	union {
>    

Please just use bool for multimapped.  If we grow more than 4 flags, we 
can use 'bool flag : 1;' to reduce space while retaining readability.

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

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