linux-kernel - Re: [PATCH 00/13] KVM: MMU: fast page fault

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Message-ID: <4F8D0D29.9050009@linux.vnet.ibm.com>
Date:	Tue, 17 Apr 2012 14:26:49 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
To:	Takuya Yoshikawa <takuya.yoshikawa@...il.com>
CC:	Avi Kivity <avi@...hat.com>, kvm-ppc@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Xiao Guangrong <xiaoguangrong.eric@...il.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH 00/13] KVM: MMU: fast page fault

On 04/16/2012 11:49 PM, Takuya Yoshikawa wrote:


> Although O(1) is actually O(1) for GET_DIRTY_LOG thread, it adds some
> overheads to page fault handling.  We may need to hold mmu_lock for properly
> handling O(1)'s write protection and ~500 write protections will not be so
> cheap.  And there is no answer to the question how to achive slot-wise write
> protection.
> 


Actually no.

We do not increase the overload on page fault for migration. The number of
page fault of O(1) is the same as write-protect all spte.

And, we can also avoid to hold mmu_lock to write-protect PML4s, we can use
a generation number, and notify mmu to update its page table when dirty-log
is enabled.

Anyway, no performance data, no truth. Let me implement it first.

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