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

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Date:   Wed, 15 Jun 2022 13:11:34 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Tim Chen <tim.c.chen@...ux.intel.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 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?

> 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?

-- 
Michal Hocko
SUSE Labs