linux-kernel - Re: [RFC PATCH v1 00/11] Manage the top tier memory in a tiered memory

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Message-ID: <CALvZod4vYiT-OnQ8gmhs+NurMV+kSFptMig4FJS7RAAcJJeDNA@mail.gmail.com>
Date:   Mon, 12 Apr 2021 07:03:27 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Yang Shi <shy828301@...il.com>
Cc:     Tim Chen <tim.c.chen@...ux.intel.com>,
        Michal Hocko <mhocko@...e.cz>,
        Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Ying Huang <ying.huang@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        David Rientjes <rientjes@...gle.com>,
        Linux MM <linux-mm@...ck.org>,
        Cgroups <cgroups@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v1 00/11] Manage the top tier memory in a tiered memory

On Thu, Apr 8, 2021 at 1:50 PM Yang Shi <shy828301@...il.com> wrote:
>
[...]

> >
> > The low and min limits have semantics similar to the v1's soft limit
> > for this situation i.e. letting the low priority job occupy top tier
> > memory and depending on reclaim to take back the excess top tier
> > memory use of such jobs.
>
> I don't get why low priority jobs can *not* use top tier memory?

I am saying low priority jobs can use top tier memory. The only
difference is to limit them upfront (using limits) or reclaim from
them later (using min/low/soft-limit).

> I can
> think of it may incur latency overhead for high priority jobs. If it
> is not allowed, it could be restricted by cpuset without introducing
> in any new interfaces.
>
> I'm supposed the memory utilization could be maximized by allowing all
> jobs allocate memory from all applicable nodes, then let reclaimer (or
> something new if needed)

Most probably something new as we do want to consider unevictable
memory as well.

> do the job to migrate the memory to proper
> nodes by time. We could achieve some kind of balance between memory
> utilization and resource isolation.
>

Tradeoff between utilization and isolation should be decided by the user/admin.