linux-kernel - Re: [PATCH v3 0/3] create sysfs representation of ACPI HMAT

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Date:   Sat, 23 Dec 2017 10:44:34 +0530
From:   Anshuman Khandual <khandual@...ux.vnet.ibm.com>
To:     Dave Hansen <dave.hansen@...el.com>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Cc:     "Anaczkowski, Lukasz" <lukasz.anaczkowski@...el.com>,
        "Box, David E" <david.e.box@...el.com>,
        "Kogut, Jaroslaw" <Jaroslaw.Kogut@...el.com>,
        "Koss, Marcin" <marcin.koss@...el.com>,
        "Koziej, Artur" <artur.koziej@...el.com>,
        "Lahtinen, Joonas" <joonas.lahtinen@...el.com>,
        "Moore, Robert" <robert.moore@...el.com>,
        "Nachimuthu, Murugasamy" <murugasamy.nachimuthu@...el.com>,
        "Odzioba, Lukasz" <lukasz.odzioba@...el.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "Schmauss, Erik" <erik.schmauss@...el.com>,
        "Verma, Vishal L" <vishal.l.verma@...el.com>,
        "Zheng, Lv" <lv.zheng@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Balbir Singh <bsingharora@...il.com>,
        Brice Goglin <brice.goglin@...il.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Jerome Glisse <jglisse@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Len Brown <lenb@...nel.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>, devel@...ica.org,
        linux-acpi@...r.kernel.org, linux-mm@...ck.org,
        linux-nvdimm@...ts.01.org
Subject: Re: [PATCH v3 0/3] create sysfs representation of ACPI HMAT

On 12/22/2017 10:43 PM, Dave Hansen wrote:
> On 12/21/2017 07:09 PM, Anshuman Khandual wrote:
>> I had presented a proposal for NUMA redesign in the Plumbers Conference this
>> year where various memory devices with different kind of memory attributes
>> can be represented in the kernel and be used explicitly from the user space.
>> Here is the link to the proposal if you feel interested. The proposal is
>> very intrusive and also I dont have a RFC for it yet for discussion here.
> I think that's the best reason to "re-use NUMA" for this: it's _not_
> intrusive.
> 
> Also, from an x86 perspective, these HMAT systems *will* be out there.
> Old versions of Linux *will* see different types of memory as separate
> NUMA nodes.  So, if we are going to do something different, it's going
> to be interesting to un-teach those systems about using the NUMA APIs
> for this.  That ship has sailed.

I understand the need to fetch these details from ACPI/DT for
applications to target these distinct memory only NUMA nodes.
This can be done by parsing from platform specific values from
/proc/acpi/ or /proc/device-tree/ interfaces. This can be a
short term solution before NUMA redesign can be figured out.
But adding generic devices like "hmat" in the /sys/devices/
path which will be locked for good, seems problematic.