linux-kernel - Re: [PATCH 0/4] [RFC] Migrate Pages in lieu of discard

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Date:   Thu, 17 Oct 2019 09:39:04 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Suleiman Souhlal <suleiman@...gle.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH 0/4] [RFC] Migrate Pages in lieu of discard

On Thu, Oct 17, 2019 at 9:32 AM Dave Hansen <dave.hansen@...el.com> wrote:
>
> On 10/17/19 9:01 AM, Suleiman Souhlal wrote:
> > One problem that came up is that if you get into direct reclaim,
> > because persistent memory can have pretty low write throughput, you
> > can end up stalling users for a pretty long time while migrating
> > pages.
>
> Basically, you're saying that memory load spikes turn into latency spikes?
>
> FWIW, we have been benchmarking this sucker with benchmarks that claim
> to care about latency.  In general, compared to DRAM, we do see worse
> latency, but nothing catastrophic yet.  I'd be interested if you have
> any workloads that act as reasonable proxies for your latency requirements.
>
> > Because of that, we moved to a solution based on the proactive reclaim
> > of idle pages, that was presented at LSFMM earlier this year:
> > https://lwn.net/Articles/787611/ .
>
> I saw the presentation.  The feedback in the room as I remember it was
> that proactive reclaim essentially replaced the existing reclaim
> mechanism, to which the audience was not receptive.  Have folks opinions
> changed on that, or are you looking for other solutions?
>

I am currently working on a solution which shares the mechanisms
between regular and proactive reclaim. The interested users/admins can
setup proactive reclaim otherwise the regular reclaim will work on low
memory. I will have something in one/two months and will post the
patches.

Shakeel