RE: [PATCH 5/5] dax: "Hotplug" persistent memory for use like normal RAM

From: "Du, Fan" <fan.du@intel.com>
To: "Williams, Dan J" <dan.j.williams@intel.com>,
	Jane Chu <jane.chu@oracle.com>
Cc: "Tom Lendacky" <thomas.lendacky@amd.com>,
	"Michal Hocko" <mhocko@suse.com>,
	linux-nvdimm <linux-nvdimm@lists.01.org>,
	"Takashi Iwai" <tiwai@suse.de>,
	"Dave Hansen" <dave.hansen@linux.intel.com>,
	"Huang, Ying" <ying.huang@intel.com>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	"Linux MM" <linux-mm@kvack.org>,
	"Jér?me Glisse" <jglisse@redhat.com>,
	"Borislav Petkov" <bp@suse.de>,
	"Yaowei Bai" <baiyaowei@cmss.chinamobile.com>,
	"Ross Zwisler" <zwisler@kernel.org>,
	"Bjorn Helgaas" <bhelgaas@google.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Wu, Fengguang" <fengguang.wu@intel.com>,
	"Du, Fan" <fan.du@intel.com>
Subject: RE: [PATCH 5/5] dax: "Hotplug" persistent memory for use like normal RAM
Date: Fri, 25 Jan 2019 08:20:45 +0000	[thread overview]
Message-ID: <5A90DA2E42F8AE43BC4A093BF067884825733A5B@SHSMSX104.ccr.corp.intel.com> (raw)
In-Reply-To: <CAPcyv4hjJhUQpMy1CVJZur0Ssr7Cr2fkcD50L5gzx6v_KY14vg@mail.gmail.com>

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?

And how about when ARS is involved but no machine check fired for the function
of this patchset?

>-----Original Message-----
>From: Linux-nvdimm [mailto:linux-nvdimm-bounces@lists.01.org] On Behalf
>Of Dan Williams
>Sent: Friday, January 25, 2019 2:28 PM
>To: Jane Chu <jane.chu@oracle.com>
>Cc: Tom Lendacky <thomas.lendacky@amd.com>; Michal Hocko
><mhocko@suse.com>; linux-nvdimm <linux-nvdimm@lists.01.org>; Takashi
>Iwai <tiwai@suse.de>; Dave Hansen <dave.hansen@linux.intel.com>; Huang,
>Ying <ying.huang@intel.com>; Linux Kernel Mailing List
><linux-kernel@vger.kernel.org>; Linux MM <linux-mm@kvack.org>; Jérôme
>Glisse <jglisse@redhat.com>; Borislav Petkov <bp@suse.de>; Yaowei Bai
><baiyaowei@cmss.chinamobile.com>; Ross Zwisler <zwisler@kernel.org>;
>Bjorn Helgaas <bhelgaas@google.com>; Andrew Morton
><akpm@linux-foundation.org>; Wu, Fengguang <fengguang.wu@intel.com>
>Subject: Re: [PATCH 5/5] dax: "Hotplug" persistent memory for use like
>normal RAM
>
>On Thu, Jan 24, 2019 at 10:13 PM Jane Chu <jane.chu@oracle.com> wrote:
>>
>> Hi, Dave,
>>
>> While chatting with my colleague Erwin about the patchset, it occurred
>> that we're not clear about the error handling part. Specifically,
>>
>> 1. If an uncorrectable error is detected during a 'load' in the hot
>> plugged pmem region, how will the error be handled?  will it be
>> handled like PMEM or DRAM?
>
>DRAM.
>
>> 2. If a poison is set, and is persistent, which entity should clear
>> the poison, and badblock(if applicable)? If it's user's responsibility,
>> does ndctl support the clearing in this mode?
>
>With persistent memory advertised via a static logical-to-physical
>storage/dax device mapping, once an error develops it destroys a
>physical *and* logical part of a device address space. That loss of
>logical address space makes error clearing a necessity. However, with
>the DRAM / "System RAM" error handling model, the OS can just offline
>the page and map a different one to repair the logical address space.
>So, no, ndctl will not have explicit enabling to clear volatile
>errors, the OS will just dynamically offline problematic pages.
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