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

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Date:   Fri, 25 Jan 2019 08:20:45 +0000
From:   "Du, Fan" <fan.du@...el.com>
To:     "Williams, Dan J" <dan.j.williams@...el.com>,
        Jane Chu <jane.chu@...cle.com>
CC:     Tom Lendacky <thomas.lendacky@....com>,
        Michal Hocko <mhocko@...e.com>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Takashi Iwai <tiwai@...e.de>,
        "Dave Hansen" <dave.hansen@...ux.intel.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Jér?me Glisse <jglisse@...hat.com>,
        Borislav Petkov <bp@...e.de>,
        Yaowei Bai <baiyaowei@...s.chinamobile.com>,
        Ross Zwisler <zwisler@...nel.org>,
        "Bjorn Helgaas" <bhelgaas@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Wu, Fengguang" <fengguang.wu@...el.com>,
        "Du, Fan" <fan.du@...el.com>
Subject: RE: [PATCH 5/5] dax: "Hotplug" persistent memory for use like
 normal RAM

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@...ts.01.org] On Behalf
>Of Dan Williams
>Sent: Friday, January 25, 2019 2:28 PM
>To: Jane Chu <jane.chu@...cle.com>
>Cc: Tom Lendacky <thomas.lendacky@....com>; Michal Hocko
><mhocko@...e.com>; linux-nvdimm <linux-nvdimm@...ts.01.org>; Takashi
>Iwai <tiwai@...e.de>; Dave Hansen <dave.hansen@...ux.intel.com>; Huang,
>Ying <ying.huang@...el.com>; Linux Kernel Mailing List
><linux-kernel@...r.kernel.org>; Linux MM <linux-mm@...ck.org>; Jérôme
>Glisse <jglisse@...hat.com>; Borislav Petkov <bp@...e.de>; Yaowei Bai
><baiyaowei@...s.chinamobile.com>; Ross Zwisler <zwisler@...nel.org>;
>Bjorn Helgaas <bhelgaas@...gle.com>; Andrew Morton
><akpm@...ux-foundation.org>; Wu, Fengguang <fengguang.wu@...el.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@...cle.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.
>_______________________________________________
>Linux-nvdimm mailing list
>Linux-nvdimm@...ts.01.org
>https://lists.01.org/mailman/listinfo/linux-nvdimm

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