From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hollis Blanchard Subject: the trouble with large pages Date: Fri, 07 Sep 2007 09:40:20 -0500 Message-ID: <1189176020.9287.18.camel@basalt> Reply-To: Hollis Blanchard Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel To: kvm-ppc-devel Return-path: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org The PowerPC 440 Linux kernel uses 256MB pages for the linear mapping. When we run that as a guest, those pages would of course need to be physically contiguous in the host. I think long-term the KVM plan is to move memory allocation out of the kernel (where it currently uses vmalloc) into userspace, with the idea being that userspace could allocate memory via hugetlbfs. Anybody tried hugetlbfs on 440 or e500? A poor-man's equivalent might be to limit the host memory to e.g. 256MB, then have userspace mmap(/dev/ram) starting there. Another possibility is to fake out guest large pages by actually using small pages on the host, and handle the extra faults in KVM without notifying the guest. -- Hollis Blanchard IBM Linux Technology Center ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/