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

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Message-ID: <CAPcyv4j2vmWXQO0QoBU5-yXBJBaEuDrPJ0t1tWkftCbwb4rnWA@mail.gmail.com>
Date:   Mon, 28 Jan 2019 08:34:56 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Jane Chu <jane.chu@...cle.com>,
        "Verma, Vishal L" <vishal.l.verma@...el.com>,
        "Du, Fan" <fan.du@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "bp@...e.de" <bp@...e.de>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "tiwai@...e.de" <tiwai@...e.de>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        "jglisse@...hat.com" <jglisse@...hat.com>,
        "zwisler@...nel.org" <zwisler@...nel.org>,
        "baiyaowei@...s.chinamobile.com" <baiyaowei@...s.chinamobile.com>,
        "thomas.lendacky@....com" <thomas.lendacky@....com>,
        "Wu, Fengguang" <fengguang.wu@...el.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>
Subject: Re: [PATCH 5/5] dax: "Hotplug" persistent memory for use like normal RAM

On Mon, Jan 28, 2019 at 1:26 AM Michal Hocko <mhocko@...nel.org> wrote:
>
> On Fri 25-01-19 11:15:08, Dan Williams wrote:
> [...]
> > 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.
>
> I am not sure I understand. Do you mean to clear HWPoison when the
> memory is hotadded (add_pages) or onlined (resp. move_pfn_range_to_zone)?

Before the memory is hot-added via the kmem driver it shows up as an
independent persistent memory namespace. A namespace can be configured
as a block device and errors cleared by writing to the given "bad
block". Once all media errors are cleared the namespace can be
assigned as volatile memory to the core-kernel mm. The memory range
starts as a namespace each boot and must be hotplugged via startup
scripts, those scripts can be made to handle the bad block pruning.