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From:   "Huang\, Ying" <ying.huang@intel.com>
To:     David Rientjes <rientjes@google.com>
Cc:     Dave Hansen <dave.hansen@intel.com>,
        Yang Shi <yang.shi@linux.alibaba.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        <linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>,
        <kbusch@kernel.org>, <dan.j.williams@intel.com>
Subject: Re: [RFC][PATCH 3/8] mm/vmscan: Attempt to migrate page in lieu of discard
References: <20200629234503.749E5340@viggo.jf.intel.com>
        <20200629234509.8F89C4EF@viggo.jf.intel.com>
        <alpine.DEB.2.22.394.2006301732010.1644114@chino.kir.corp.google.com>
        <039a5704-4468-f662-d660-668071842ca3@linux.alibaba.com>
        <alpine.DEB.2.22.394.2006302208460.1685201@chino.kir.corp.google.com>
        <87h7urlioe.fsf@yhuang-dev.intel.com>
        <8182ede7-88ce-b891-d100-8c036130797e@intel.com>
        <alpine.DEB.2.23.453.2007011248580.1908531@chino.kir.corp.google.com>
Date:   Thu, 02 Jul 2020 09:50:51 +0800
In-Reply-To: <alpine.DEB.2.23.453.2007011248580.1908531@chino.kir.corp.google.com>
        (David Rientjes's message of "Wed, 1 Jul 2020 12:50:23 -0700")
Message-ID: <87v9j6k7lw.fsf@yhuang-dev.intel.com>
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David Rientjes <rientjes@google.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