From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f44.google.com (mail-pa0-f44.google.com [209.85.220.44]) by kanga.kvack.org (Postfix) with ESMTP id 433CC6B0253 for ; Fri, 9 Oct 2015 14:51:37 -0400 (EDT) Received: by pablk4 with SMTP id lk4so93789098pab.3 for ; Fri, 09 Oct 2015 11:51:37 -0700 (PDT) Received: from mga01.intel.com (mga01.intel.com. [192.55.52.88]) by mx.google.com with ESMTP id kz9si4501505pbc.150.2015.10.09.11.51.36 for ; Fri, 09 Oct 2015 11:51:36 -0700 (PDT) From: "Luck, Tony" Subject: RE: [PATCH][RFC] mm: Introduce kernelcore=reliable option Date: Fri, 9 Oct 2015 18:51:34 +0000 Message-ID: <3908561D78D1C84285E8C5FCA982C28F32B523DB@ORSMSX114.amr.corp.intel.com> References: <1444402599-15274-1-git-send-email-izumi.taku@jp.fujitsu.com> <561762DC.3080608@huawei.com> <561787DA.4040809@jp.fujitsu.com> <5617989E.9070700@huawei.com> <5617D878.5060903@intel.com> In-Reply-To: <5617D878.5060903@intel.com> Content-Language: en-US Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Sender: owner-linux-mm@kvack.org List-ID: To: "Hansen, Dave" , Xishi Qiu , Kamezawa Hiroyuki Cc: Taku Izumi , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "mel@csn.ul.ie" , "akpm@linux-foundation.org" , Mel Gorman , Ingo Molnar , "zhongjiang@huawei.com" > I understand if the mirrored regions are always at the start of the zone > today, but is that somehow guaranteed going forward on all future hardwar= e? > > I think it's important to at least consider what we would do if DMA32 > turned out to be non-reliable. Current hardware can map one mirrored region from each memory controller. We have two memory controllers per socket. So on a 4-socket machine we wil= l usually have 8 separate mirrored ranges. Two per NUMA node (assuming cluster on die is not enabled). Practically I think it is safe to assume that any sane configuration will a= lways choose to mirror the <4GB range: 1) It's a trivial percentage of total memory on a system that supports mirr= or (2GB[1] out of my, essentially minimal, 512GB[2] machine). So 0.4% ... why = would you not mirror it? 2) It contains a bunch of things that you are likely to want mirrored. Curr= ently our boot loaders put the kernel there (don't they??). All sorts of BIOS spa= ce that might be accessed at any time by SMI is there. BUT ... we might want the kernel to ignore its mirrored status precisely be= cause we want to make sure that anyone who really needs DMA or DMA32 allocations is not prevented from using it. -Tony [*] 2GB-4GB is MMIO space, so only 2GB of actual memory below the 4GB line. [2] Big servers should always have at least one DIMM populated in every cha= nnel to provide enough memory bandwidth to feed all the cores. This machine has 4 sockets * 2 memory controllers * 4 channels =3D 32 total. Fill them with = a single 16GB DIMM each gives 512G. Big systems can use larger DIMMs, and fill up to 3 DIMMS on each channel. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org