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

From: Shakeel Butt
Date: Thu Oct 17 2019 - 12:39:21 EST

On Thu, Oct 17, 2019 at 9:32 AM Dave Hansen <dave.hansen@xxxxxxxxx> 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:
> > .
> 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