From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965531AbbDVPZm (ORCPT ); Wed, 22 Apr 2015 11:25:42 -0400 Received: from resqmta-ch2-10v.sys.comcast.net ([69.252.207.42]:50569 "EHLO resqmta-ch2-10v.sys.comcast.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965450AbbDVPZk (ORCPT ); Wed, 22 Apr 2015 11:25:40 -0400 Date: Wed, 22 Apr 2015 10:25:37 -0500 (CDT) From: Christoph Lameter X-X-Sender: cl@gentwo.org To: Benjamin Herrenschmidt cc: paulmck@linux.vnet.ibm.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, jglisse@redhat.com, mgorman@suse.de, aarcange@redhat.com, riel@redhat.com, airlied@redhat.com, aneesh.kumar@linux.vnet.ibm.com, Cameron Buschardt , Mark Hairgrove , Geoffrey Gerfin , John McKenna , akpm@linux-foundation.org Subject: Re: Interacting with coherent memory on external devices In-Reply-To: <1429664686.27410.84.camel@kernel.crashing.org> Message-ID: References: <20150421214445.GA29093@linux.vnet.ibm.com> <1429663372.27410.75.camel@kernel.crashing.org> <20150422005757.GP5561@linux.vnet.ibm.com> <1429664686.27410.84.camel@kernel.crashing.org> Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 22 Apr 2015, Benjamin Herrenschmidt wrote: > Right, it doesn't look at all like what we want. Its definitely a way to map memory that is outside of the kernel managed pool into a user space process. For that matter any device driver could be doing this as well. The point is that we already have pletora of features to do this. Putting new requirements on the already warped-and-screwed-up-beyond-all-hope zombie of a page allocator that we have today is not the way to do this. In particular what I have head repeatedly is that we do not want kernel structures alllocated there but then we still want to use this because we want malloc support in libraries. The memory has different performance characteristics (for starters there may be lots of other isssues depending on the device) so we just add a NUMA "node" with estremely high distance. There are hooks in glibc where you can replace the memory management of the apps if you want that.