linux-kernel - Re: [RFC PATCH v2 0/3] mm: mempolicy: Multi-tier weighted interleaving

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Message-ID: <ZTlxxR0ntEzBPwre@memverge.com>
Date:   Wed, 25 Oct 2023 15:51:33 -0400
From:   Gregory Price <gregory.price@...verge.com>
To:     "Huang, Ying" <ying.huang@...el.com>
Cc:     Gregory Price <gourry.memverge@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-cxl@...r.kernel.org,
        akpm@...ux-foundation.org, sthanneeru@...ron.com,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Wei Xu <weixugc@...gle.com>,
        Alistair Popple <apopple@...dia.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Michal Hocko <mhocko@...nel.org>,
        Tim Chen <tim.c.chen@...el.com>, Yang Shi <shy828301@...il.com>
Subject: Re: [RFC PATCH v2 0/3] mm: mempolicy: Multi-tier weighted
 interleaving

On Wed, Oct 25, 2023 at 09:13:01AM +0800, Huang, Ying wrote:
> Gregory Price <gregory.price@...verge.com> writes:
> 
> > On Mon, Oct 23, 2023 at 10:09:56AM +0800, Huang, Ying wrote:
> >> Gregory Price <gregory.price@...verge.com> writes:
> >> 
> >> > Depends.  if a user explicitly launches with `numactl --cpunodebind=0`
> >> > then yes, you can force a task (and all its children) to run on node0.
> >> 
> >> IIUC, in your example, the `numactl` command line will be
> >> 
> >>   numactl --cpunodebind=0 --weighted-interleave=0,1,2,3
> >> 
> >> That is, the CPU is restricted to node 0, while memory is distributed to
> >> all nodes.  This doesn't sound like reasonable for me.
> >> 
> >
> > It being reasonable isn't really relevant. You can do this today with
> > normal interleave:
> >
> > numactl --cpunodebind=0 --interleave=0,1,2,3
> >
> > The only difference between this method and that is the application of
> > weights.  Doesn't seem reasonable to lock users out of doing it.
> 
> Do you have some real use case?
> 

I don't, but this is how mempolicy and numactl presently work.  You can
do this today with the current kernel.  I'm simply extending it to
include weights.

~Gregory