linux-kernel - Re: RFC: Memory Tiering Kernel Interfaces

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Date:   Tue, 3 May 2022 10:47:20 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Alistair Popple <apopple@...dia.com>,
        Davidlohr Bueso <dave@...olabs.net>
Cc:     Wei Xu <weixugc@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Huang Ying <ying.huang@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Yang Shi <shy828301@...il.com>, Linux MM <linux-mm@...ck.org>,
        Greg Thelen <gthelen@...gle.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Jagdish Gediya <jvgediya@...ux.ibm.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...nel.org>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Brice Goglin <brice.goglin@...il.com>,
        Feng Tang <feng.tang@...el.com>, Jonathan.Cameron@...wei.com
Subject: Re: RFC: Memory Tiering Kernel Interfaces

On 5/3/22 10:14, Alistair Popple wrote:
> I would certainly be interested in figuring out how HW could provide some sort
> of heatmap to identify which pages are hot and which processing unit is using
> them. Currently for these systems users have to manually assign memory policy to
> get any reasonable performance, both to disable NUMA balancing and make sure
> memory is allocated on the right node.

Autonuma-induced page faults are a total non-starter for lots of
workloads, even ignoring GPUs.  Basically anyone who is latency
sensitive stays far, far away from autonuma.

As for improving on page faults for data collection...

*Can* hardware provide this information?  Definitely.

Have hardware vendors been motivated enough to add hardware to do this?
 Nope, not yet.

Do you know anyone that works for any hardware companies? ;)

Seriously, though.  Folks at Intel _are_ thinking about this problem.
I'm hoping we have hardware some day to help lend a hand.  The more
hardware vendors that do this, the more likely it is that we'll have
good kernel code to consume data from the hardware.