linux-kernel - Re: [RFC][PATCH 3/8] mm/vmscan: Attempt to migrate page in lieu of discard

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Date:   Thu, 02 Jul 2020 09:50:51 +0800
From:   "Huang\, Ying" <ying.huang@...el.com>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <kbusch@...nel.org>, <dan.j.williams@...el.com>
Subject: Re: [RFC][PATCH 3/8] mm/vmscan: Attempt to migrate page in lieu of discard

David Rientjes <rientjes@...gle.com> writes:

> On Wed, 1 Jul 2020, Dave Hansen wrote:
>
>> Even if they don't allocate directly from PMEM, is it OK for such an app
>> to get its cold data migrated to PMEM?  That's a much more subtle
>> question and I suspect the kernel isn't going to have a single answer
>> for it.  I suspect we'll need a cpuset-level knob to turn auto-demotion
>> on or off.
>> 
>
> I think the answer is whether the app's cold data can be reclaimed, 
> otherwise migration to PMEM is likely better in terms of performance.  So 
> any such app today should just be mlocking its cold data if it can't 
> handle overhead from reclaim?

Yes.  That's a way to solve the problem.  A cpuset-level knob may be
more flexible, because you don't need to change the application source
code.

Best Regards,
Huang, Ying