From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752060AbWIXCO0 (ORCPT ); Sat, 23 Sep 2006 22:14:26 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752061AbWIXCO0 (ORCPT ); Sat, 23 Sep 2006 22:14:26 -0400 Received: from omx2-ext.sgi.com ([192.48.171.19]:34714 "EHLO omx2.sgi.com") by vger.kernel.org with ESMTP id S1752060AbWIXCOZ (ORCPT ); Sat, 23 Sep 2006 22:14:25 -0400 Date: Sat, 23 Sep 2006 19:13:53 -0700 (PDT) From: Christoph Lameter To: Andi Kleen cc: Martin Bligh , Alan Cox , akpm@google.com, linux-kernel@vger.kernel.org, Christoph Hellwig , James Bottomley , linux-mm@kvack.org Subject: Re: More thoughts on getting rid of ZONE_DMA In-Reply-To: <200609230134.45355.ak@suse.de> Message-ID: References: <4514441E.70207@mbligh.org> <200609230134.45355.ak@suse.de> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 23 Sep 2006, Andi Kleen wrote: > The problem is that if someone has a workload with lots of pinned pages > (e.g. lots of mlock) then the first 16MB might fill up completely and there > is no chance at all to free it because it's pinned Note that mlock'ed pages are movable. mlock only specifies that pages must stay in memory. It does not say that they cannot be moved. So page migration could help there. This brings up a possible problem spot in the current kernel: It seems that the VM is capable of migrating pages from ZONE_DMA to ZONE_NORMAL! So once pages are in memory then they may move out of the DMA-able area. I assume the writeback paths have some means of detecting that a page is out of range during writeback and then do page bouncing? If that is the case then we could simply move movable pages out if necessary. That would be a kind of bouncing logic there that would only kick in if necessary.