linux-kernel - Re: [RFC PATCH 0/3] Cgroup accounting of memory tier usage

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Date:   Wed, 15 Jun 2022 08:23:56 -0700
From:   Tim Chen <tim.c.chen@...ux.intel.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org,
        Wei Xu <weixugc@...gle.com>, Huang Ying <ying.huang@...el.com>,
        Greg Thelen <gthelen@...gle.com>,
        Yang Shi <shy828301@...il.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Brice Goglin <brice.goglin@...il.com>,
        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 13:11 +0200, Michal Hocko wrote:
> On Tue 14-06-22 15:25:32, 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.
> 
> I guess you meant cgroupfs here, right?

Yes.

> 
> > 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
> > (3) There are use cases not covered by (1) and (2). 
> 
> I would start by asking why do we need a dedicated interface in the
> first place. Why the existing numa_stat is not a proper interface. Right
> now we only report LRU per node stats. Is this insufficient?
> What is userspace expect to do based on the reported data?

Exporting the toptier information here is convenient for me for debugging
purpose of seeing whether a cgroup's toptier usage is under control.
Otherwise writing a script to parse numastat and the memtier heirachy will
work too. Exporting toptier usage directly is optional and we don't have to do it.

Tim