linux-kernel - Re: [HMM-v25 19/19] mm/hmm: add new helper to hotplug CDM memory region v3

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Message-ID: <CAAsGZS67JqVJYMMuPchz6zDr36JOdQK=+LQ8RPKKbQm-wsV4Vw@mail.gmail.com>
Date:   Thu, 16 Nov 2017 19:47:40 -0800
From:   chetan L <loke.chetan@...il.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Bob Liu <liubo95@...wei.com>, Jerome Glisse <jglisse@...hat.com>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        John Hubbard <jhubbard@...dia.com>,
        David Nellans <dnellans@...dia.com>,
        Balbir Singh <bsingharora@...il.com>,
        majiuyue <majiuyue@...wei.com>,
        "xieyisheng (A)" <xieyisheng1@...wei.com>
Subject: Re: [HMM-v25 19/19] mm/hmm: add new helper to hotplug CDM memory
 region v3

On Fri, Sep 8, 2017 at 1:43 PM, Dan Williams <dan.j.williams@...el.com> wrote:
> On Thu, Sep 7, 2017 at 6:59 PM, Bob Liu <liubo95@...wei.com> wrote:
>> On 2017/9/8 1:27, Jerome Glisse wrote:
> [..]
>>> No this are 2 orthogonal thing, they do not conflict with each others quite
>>> the contrary. HMM (the CDM part is no different) is a set of helpers, see
>>> it as a toolbox, for device driver.
>>>
>>> HMAT is a way for firmware to report memory resources with more informations
>>> that just range of physical address. HMAT is specific to platform that rely
>>> on ACPI. HMAT does not provide any helpers to manage these memory.
>>>
>>> So a device driver can get informations about device memory from HMAT and then
>>> use HMM to help in managing and using this memory.
>>>
>>
>> Yes, but as Balbir mentioned requires :
>> 1. Don't online the memory as a NUMA node
>> 2. Use the HMM-CDM API's to map the memory to ZONE DEVICE via the driver
>>
>> And I'm not sure whether Intel going to use this HMM-CDM based method for their "target domain" memory ?
>> Or they prefer to NUMA approach?   Ross？ Dan?
>
> The starting / strawman proposal for performance differentiated memory
> ranges is to get platform firmware to mark them reserved by default.
> Then, after we parse the HMAT, make them available via the device-dax
> mechanism so that applications that need 100% guaranteed access to
> these potentially high-value / limited-capacity ranges can be sure to
> get them by default, i.e. before any random kernel objects are placed
> in them. Otherwise, if there are no dedicated users for the memory
> ranges via device-dax, or they don't need the total capacity, we want
> to hotplug that memory into the general purpose memory allocator with
> a numa node number so typical numactl and memory-management flows are
> enabled.
>
> Ideally this would not be specific to HMAT and any agent that knows
> differentiated performance characteristics of a memory range could use
> this scheme.

@Dan/Ross

With this approach, in a SVM environment, if you would want a PRI(page
grant) request to get satisfied from this HMAT-indexed memory node,
then do you think we could make that happen. If yes, is that something
you guys are currently working on.


Chetan