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

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Date:   Thu, 17 Oct 2019 09:32:02 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Suleiman Souhlal <suleiman@...gle.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     Linux Kernel <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
        dan.j.williams@...el.com
Subject: Re: [PATCH 0/4] [RFC] Migrate Pages in lieu of discard

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?