linux-kernel - Re: [PATCH 5/6] KVM: Separate rmap_pde from kvm_lpage_info->write

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Message-Id: <20120628124546.83a829f3.yoshikawa.takuya@oss.ntt.co.jp>
Date:	Thu, 28 Jun 2012 12:45:46 +0900
From:	Takuya Yoshikawa <yoshikawa.takuya@....ntt.co.jp>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Cc:	avi@...hat.com, mtosatti@...hat.com, agraf@...e.de,
	paulus@...ba.org, aarcange@...hat.com, kvm@...r.kernel.org,
	kvm-ppc@...r.kernel.org, linux-kernel@...r.kernel.org,
	takuya.yoshikawa@...il.com
Subject: Re: [PATCH 5/6] KVM: Separate rmap_pde from
 kvm_lpage_info->write_count

On Thu, 28 Jun 2012 11:12:51 +0800
Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com> wrote:

> >  struct kvm_arch_memory_slot {
> > +	unsigned long *rmap_pde[KVM_NR_PAGE_SIZES - 1];
> >  	struct kvm_lpage_info *lpage_info[KVM_NR_PAGE_SIZES - 1];
> >  };
> > 
> 
> It looks little complex than before - need manage more alloc-ed/freed buffers.

Actually I want to integrate rmap and rmap_pde in the future:

	rmap[KVM_NR_PAGE_SIZES]

For this we need to modify some unrelated ppc code, so I just
avoided the integration in this series.

Note: write_count: 4 bytes, rmap_pde: 8 bytes.  So we are wasting
extra paddings by packing them into lpage_info.

> Why not just introduce a function to get the next rmap? Something like this:

I want to eliminate this kind of overheads.

Thanks,
	Takuya

> static unsigned long *get_next_rmap(unsigned long *rmap, int level)
> {
> 	struct kvm_lpage_info *linfo
> 
> 	if (level == 1)
> 		return rmap++
> 	
> 	linfo = container_of(rmap, struct kvm_lpage_info, rmap_pde);
> 	
> 	return &(++linfo)->rmap_pde
> }
> 
> [ Completely untested ]
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