From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH v3 11/11] KVM: MMU: improve write flooding detected Date: Tue, 13 Sep 2011 14:07:06 +0300 Message-ID: <4E6F395A.5030609@redhat.com> References: <4E5C4C20.3000403@cn.fujitsu.com> <4E5C4D17.2080700@cn.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Marcelo Tosatti , LKML , KVM To: Xiao Guangrong Return-path: In-Reply-To: <4E5C4D17.2080700@cn.fujitsu.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 08/30/2011 05:38 AM, Xiao Guangrong wrote: > Detecting write-flooding does not work well, when we handle page written, if > the last speculative spte is not accessed, we treat the page is > write-flooding, however, we can speculative spte on many path, such as pte > prefetch, page synced, that means the last speculative spte may be not point > to the written page and the written page can be accessed via other sptes, so > depends on the Accessed bit of the last speculative spte is not enough > > Instead of detected page accessed, we can detect whether the spte is accessed > after it is written, if the spte is not accessed but it is written frequently, > we treat is not a page table or it not used for a long time > > The spte may not be accessed, but other sptes in the same page can be accessed. An example is the fixmap area for kmap_atomic(), there will be a lot of pte writes but other sptes will be accessed without going through soft-mmu at all. I think you have to read the parent_ptes->spte.accessed bits to be sure. -- error compiling committee.c: too many arguments to function