From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 40EE0C282C0 for ; Fri, 25 Jan 2019 23:32:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 09273218D0 for ; Fri, 25 Jan 2019 23:32:40 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="CayHidDM" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729489AbfAYXci (ORCPT ); Fri, 25 Jan 2019 18:32:38 -0500 Received: from userp2120.oracle.com ([156.151.31.85]:47316 "EHLO userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726218AbfAYXci (ORCPT ); Fri, 25 Jan 2019 18:32:38 -0500 Received: from pps.filterd (userp2120.oracle.com [127.0.0.1]) by userp2120.oracle.com (8.16.0.22/8.16.0.22) with SMTP id x0PNTTvW187710; Fri, 25 Jan 2019 23:30:17 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=subject : to : cc : references : from : message-id : date : mime-version : in-reply-to : content-type : content-transfer-encoding; s=corp-2018-07-02; bh=khFM13MUGmAuQcjDxhffkILU91NaQU/s+UehyBZeQ3A=; b=CayHidDM0AsIhq1es1p8MmosDeNO+UA6SWtjm5JdZHv57dAd8E9+sDo+vtOnN3UdSH4d yD4mu22fDmf6erYVSyYFIaXfaKYAdYI9RE8mBAXDRh80l3DbG0tI+2WNAlVegicmY46Z +7HFu4fbbeCKStTPmJB+htg6tza8Ey0RShycWudRnae+LLomglsEk9cEazySlzJQKevQ jnw8O3wKwOlYWm/D53/F3XrxV9yWTWIEZ9IsrbO4AvNciiWCfuAVCez9CKu6uoGr5+I9 9lFA26YSq/7Hh/48h7prg/ImyQTQDSnWv42dSJffa773PK2Fa4E25S5F7bjXrRFHFuJ2 ig== Received: from aserv0022.oracle.com (aserv0022.oracle.com [141.146.126.234]) by userp2120.oracle.com with ESMTP id 2q3vhs897m-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 25 Jan 2019 23:30:17 +0000 Received: from aserv0122.oracle.com (aserv0122.oracle.com [141.146.126.236]) by aserv0022.oracle.com (8.14.4/8.14.4) with ESMTP id x0PNUGmN005973 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 25 Jan 2019 23:30:16 GMT Received: from abhmp0016.oracle.com (abhmp0016.oracle.com [141.146.116.22]) by aserv0122.oracle.com (8.14.4/8.14.4) with ESMTP id x0PNUDIA015302; Fri, 25 Jan 2019 23:30:13 GMT Received: from [10.159.149.153] (/10.159.149.153) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Fri, 25 Jan 2019 15:30:13 -0800 Subject: Re: [PATCH 5/5] dax: "Hotplug" persistent memory for use like normal RAM To: Dan Williams Cc: "Verma, Vishal L" , "Du, Fan" , "linux-kernel@vger.kernel.org" , "bp@suse.de" , "linux-mm@kvack.org" , "dave.hansen@linux.intel.com" , "tiwai@suse.de" , "akpm@linux-foundation.org" , "linux-nvdimm@lists.01.org" , "jglisse@redhat.com" , "zwisler@kernel.org" , "mhocko@suse.com" , "baiyaowei@cmss.chinamobile.com" , "thomas.lendacky@amd.com" , "Wu, Fengguang" , "Huang, Ying" , "bhelgaas@google.com" References: <20190124231441.37A4A305@viggo.jf.intel.com> <20190124231448.E102D18E@viggo.jf.intel.com> <0852310e-41dc-dc96-2da5-11350f5adce6@oracle.com> <5A90DA2E42F8AE43BC4A093BF067884825733A5B@SHSMSX104.ccr.corp.intel.com> From: Jane Chu Organization: Oracle Corporation Message-ID: Date: Fri, 25 Jan 2019 15:30:10 -0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9147 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1901250178 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/25/2019 11:15 AM, Dan Williams wrote: > On Fri, Jan 25, 2019 at 11:10 AM Jane Chu wrote: >> >> >> On 1/25/2019 10:20 AM, Verma, Vishal L wrote: >>> >>> On Fri, 2019-01-25 at 09:18 -0800, Dan Williams wrote: >>>> On Fri, Jan 25, 2019 at 12:20 AM Du, Fan wrote: >>>>> Dan >>>>> >>>>> Thanks for the insights! >>>>> >>>>> Can I say, the UCE is delivered from h/w to OS in a single way in >>>>> case of machine >>>>> check, only PMEM/DAX stuff filter out UC address and managed in its >>>>> own way by >>>>> badblocks, if PMEM/DAX doesn't do so, then common RAS workflow will >>>>> kick in, >>>>> right? >>>> >>>> The common RAS workflow always kicks in, it's just the page state >>>> presented by a DAX mapping needs distinct handling. Once it is >>>> hot-plugged it no longer needs to be treated differently than "System >>>> RAM". >>>> >>>>> And how about when ARS is involved but no machine check fired for >>>>> the function >>>>> of this patchset? >>>> >>>> The hotplug effectively disconnects this address range from the ARS >>>> results. They will still be reported in the libnvdimm "region" level >>>> badblocks instance, but there's no safe / coordinated way to go clear >>>> those errors without additional kernel enabling. There is no "clear >>>> error" semantic for "System RAM". >>>> >>> Perhaps as future enabling, the kernel can go perform "clear error" for >>> offlined pages, and make them usable again. But I'm not sure how >>> prepared mm is to re-accept pages previously offlined. >>> >> >> Offlining a DRAM backed page due to an UC makes sense because >> a. the physical DRAM cell might still have an error >> b. power cycle, scrubing could potentially 'repair' the DRAM cell, >> making the page usable again. >> >> But for a PMEM backed page, neither is true. If a poison bit is set in >> a page, that indicates the underlying hardware has completed the repair >> work, all that's left is for software to recover. Secondly, because >> poison is persistent, unless software explicitly clear the bit, >> the page is permanently unusable. > > Not permanently... system-owner always has the option to use the > device-DAX and ARS mechanisms to clear errors at the next boot. > There's just no kernel enabling to do that automatically as a part of > this patch set. > > However, we should consider this along with the userspace enabling to > control which device-dax instances are set aside for hotplug. It would > make sense to have a "clear errors before hotplug" configuration > option. > Agreed, it would be nice to clear error prior to the hotplug operation, better if that can be handled by the kernel. thanks, -jane