From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762544AbYFGRiw (ORCPT ); Sat, 7 Jun 2008 13:38:52 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754297AbYFGRin (ORCPT ); Sat, 7 Jun 2008 13:38:43 -0400 Received: from gw.goop.org ([64.81.55.164]:60991 "EHLO mail.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753932AbYFGRin (ORCPT ); Sat, 7 Jun 2008 13:38:43 -0400 Message-ID: <484AC779.1070803@goop.org> Date: Sat, 07 Jun 2008 18:38:01 +0100 From: Jeremy Fitzhardinge User-Agent: Thunderbird 2.0.0.14 (X11/20080501) MIME-Version: 1.0 To: Nick Piggin CC: Linux Memory Management List , Linux Kernel Mailing List Subject: Re: [rfc][patch] mm: vmap rewrite References: <20080605102015.GA11366@wotan.suse.de> In-Reply-To: <20080605102015.GA11366@wotan.suse.de> X-Enigmail-Version: 0.95.6 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Nick Piggin wrote: > Hi. RFC. > > Rewrite the vmap allocator to use rbtrees and lazy tlb flushing, and provide a > fast, scalable percpu frontend for small vmaps. > > XEN and PAT and such do not like deferred TLB flushing. They just need to call > vm_unmap_aliases() in order to flush any deferred mappings. That call is very > expensive (well, actually not a lot more expensive than a single vunmap under > the old scheme), however it should be OK if not called too often. > What are the performance characteristics? Can it be fast-pathed if there are no outstanding aliases? For Xen, I'd need to do the alias unmap each time it allocates a page for use in a pagetable. For initial process construction that could be deferred, but creating mappings on a live process could get fairly expensive as a result. The ideal interface for me would be a way of testing if a given page has vmap aliases, so that we need only do the unmap if really necessary. I'm guessing that goes into "need a new page flag" territory though... J