From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: Regarding page table management changes from Xen v1to Xen v2 (and v3) Date: Wed, 26 Apr 2006 13:15:25 -0500 Message-ID: <444FB8BD.4070708@us.ibm.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Ian Pratt Cc: xen-devel@lists.xensource.com, Himanshu Raj List-Id: xen-devel@lists.xenproject.org Ian Pratt wrote: >> In another example, mmapped access to a file, the new >> approach will incur these two extra faults for every page >> fault required to bring a file page to page cache, right? >> > > No, these singleton updates on the Linux demand fault path are issued > with the update_va_mapping hypercall. This is possible because the > virtual address that the pte maps is known, so its possible for Xen to > use a linear pagetable to do the update rather than creating an > on-demand mapping to the domain's pagetable page. This is an important > optimization on 32b where Xen address space is tight. > Just to make sure I understand, we do the linear mapping for performance (so we don't have to keep remapping) but not necessarily to save VA space since the linear mapping uses a fixed amount of space. Is there any reason that we would strictly require a linear mapping (other than it being convenient)? Thanks, Anthony Liguori > Ian > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xensource.com > http://lists.xensource.com/xen-devel >