Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753226AbbD0Qvy (ORCPT ); Mon, 27 Apr 2015 12:51:54 -0400 Received: from resqmta-ch2-01v.sys.comcast.net ([69.252.207.33]:54728 "EHLO resqmta-ch2-01v.sys.comcast.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753087AbbD0Qvx (ORCPT ); Mon, 27 Apr 2015 12:51:53 -0400 Date: Mon, 27 Apr 2015 11:51:51 -0500 (CDT) From: Christoph Lameter X-X-Sender: cl@gentwo.org To: Jerome Glisse cc: "Paul E. McKenney" , Benjamin Herrenschmidt , 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: <20150427164325.GB26980@gmail.com> Message-ID: References: <20150424164325.GD3840@gmail.com> <20150424171957.GE3840@gmail.com> <20150424192859.GF3840@gmail.com> <20150425114633.GI5561@linux.vnet.ibm.com> <20150427154728.GA26980@gmail.com> <20150427164325.GB26980@gmail.com> Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1851 Lines: 33 On Mon, 27 Apr 2015, Jerome Glisse wrote: > > Well lets avoid that. Access to device memory comparable to what the > > drivers do today by establishing page table mappings or a generalization > > of DAX approaches would be the most straightforward way of implementing it > > and would build based on existing functionality. Page migration currently > > does not work with driver mappings or DAX because there is no struct page > > that would allow the lockdown of the page. That may require either > > continued work on the DAX with page structs approach or new developments > > in the page migration logic comparable to the get_user_page() alternative > > of simply creating a scatter gather table to just submit a couple of > > memory ranges to the I/O subsystem thereby avoiding page structs. > > What you refuse to see is that DAX is geared toward filesystem and as such > rely on special mapping. There is a reason why dax.c is in fs/ and not mm/ > and i keep pointing out we do not want our mecanism to be perceive as fs > from userspace point of view. We want to be below the fs, at the mm level > where we could really do thing transparently no matter what kind of memory > we are talking about (anonymous, file mapped, share). Ok that is why I mentioned the device memory mappings that are currently used for this purpose. You could generalize the DAX approach (which I understand as providing rw mappings to memory outside of the memory managed by the kernel and not as a fs specific thing). We can drop the DAX name and just talk about mapping to external memory if that confuses the issue. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/