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Message-ID: <64e3e50508b0bf27ed5d6957161e2b3631c1164b.camel@linux.intel.com>
Date: Wed, 15 Jun 2022 10:47:11 -0700
From: Tim Chen <tim.c.chen@...ux.intel.com>
To: Ying Huang <ying.huang@...el.com>, linux-mm@...ck.org,
akpm@...ux-foundation.org
Cc: Wei Xu <weixugc@...gle.com>, Greg Thelen <gthelen@...gle.com>,
Yang Shi <shy828301@...il.com>,
Davidlohr Bueso <dave@...olabs.net>,
Brice Goglin <brice.goglin@...il.com>,
Michal Hocko <mhocko@...nel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Hesham Almatary <hesham.almatary@...wei.com>,
Dave Hansen <dave.hansen@...el.com>,
Jonathan Cameron <Jonathan.Cameron@...wei.com>,
Alistair Popple <apopple@...dia.com>,
Dan Williams <dan.j.williams@...el.com>,
Feng Tang <feng.tang@...el.com>,
Jagdish Gediya <jvgediya@...ux.ibm.com>,
Baolin Wang <baolin.wang@...ux.alibaba.com>,
David Rientjes <rientjes@...gle.com>,
"Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
Shakeel Butt <shakeelb@...gle.com>
Subject: Re: [RFC PATCH 0/3] Cgroup accounting of memory tier usage
On Wed, 2022-06-15 at 12:58 +0800, Ying Huang wrote:
> On Tue, 2022-06-14 at 15:25 -0700, Tim Chen wrote:
> > For controlling usage of a top tiered memory by a cgroup, accounting
> > of top tier memory usage is needed. This patch set implements the
> > following:
> >
> > Patch 1 introduces interface and simple implementation to retrieve
> > cgroup tiered memory usage
> > Patch 2 introduces more efficient accounting with top tier memory page counter
> > Patch 3 provides a sysfs interface to repot the the top tiered memory
> > usage.
> >
> > The patchset works with Aneesh's v6 memory-tiering implementation [1].
> > It is a preparatory patch set before introducing features to
> > control top tiered memory in cgroups.
> >
> > I'll like to first get feedback to see if
> > (1) Controllng the topmost tiered memory is enough
> > or
> > (2) Multiple tiers at the top levels need to be grouped into "toptier"
> > or
>
> If we combine top-N tiers, I think the better name could be "fast-tier",
> in contrast to "slow-tier".
>
I can see use cases for grouping tiers. For example, it makese sense for HBM and
DRAM tiers be grouped together into a "fast-tier-group".
To make things simple, we can define any tiers above or equal
to the rank of DRAM will belong to this fast-tier-group.
An implication for page promotion/demotion is it needs
to take tier grouping into consideration. You want to demote
pages away from current tier-group. For example,
you want to demote HBM (fast-tier-group) into PMEM (slow-tier-group)
instead of into DRAM (fast-tier-group).
The question is whether fast/slow tier groups are sufficient.
Or you need fast/slow/slower groups?
> > (3) There are use cases not covered by (1) and (2).
>
> Is it necessary to control memory usage of each tier (except the
> lowest/slowest)? I am not the right person to answer the question, but
> I want to ask it.
>
I have the same question.
Tim
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