linux-kernel - Re: [RFC][PATCH v2 01/21] e820: cheat PMEM as DRAM

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Message-ID: <CAPcyv4hBBvcHiUSU4ER6WV7Po_GEwDjFcJy2aE3VW5Nwiu+Qyw@mail.gmail.com>
Date:   Wed, 26 Dec 2018 21:13:41 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Fengguang Wu <fengguang.wu@...el.com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Fan Du <fan.du@...el.com>, KVM list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Yao Yuan <yuan.yao@...el.com>,
        Peng Dong <dongx.peng@...el.com>,
        Huang Ying <ying.huang@...el.com>,
        Liu Jingqi <jingqi.liu@...el.com>,
        Dong Eddie <eddie.dong@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Zhang Yi <yi.z.zhang@...ux.intel.com>
Subject: Re: [RFC][PATCH v2 01/21] e820: cheat PMEM as DRAM

On Wed, Dec 26, 2018 at 8:11 PM Fengguang Wu <fengguang.wu@...el.com> wrote:
>
> On Wed, Dec 26, 2018 at 07:41:41PM -0800, Matthew Wilcox wrote:
> >On Wed, Dec 26, 2018 at 09:14:47PM +0800, Fengguang Wu wrote:
> >> From: Fan Du <fan.du@...el.com>
> >>
> >> This is a hack to enumerate PMEM as NUMA nodes.
> >> It's necessary for current BIOS that don't yet fill ACPI HMAT table.
> >>
> >> WARNING: take care to backup. It is mutual exclusive with libnvdimm
> >> subsystem and can destroy ndctl managed namespaces.
> >
> >Why depend on firmware to present this "correctly"?  It seems to me like
> >less effort all around to have ndctl label some namespaces as being for
> >this kind of use.
>
> Dave Hansen may be more suitable to answer your question. He posted
> patches to make PMEM NUMA node coexist with libnvdimm and ndctl:
>
> [PATCH 0/9] Allow persistent memory to be used like normal RAM
> https://lkml.org/lkml/2018/10/23/9
>
> That depends on future BIOS. So we did this quick hack to test out
> PMEM NUMA node for the existing BIOS.

No, it does not depend on a future BIOS.

Willy, have a look here [1], here [2], and here [3] for the
work-in-progress ndctl takeover approach (actually 'daxctl' in this
case).

[1]: https://lkml.org/lkml/2018/10/23/9
[2]: https://lkml.org/lkml/2018/10/31/243
[3]: https://lists.01.org/pipermail/linux-nvdimm/2018-November/018677.html