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Date:   Thu, 25 Apr 2019 10:43:02 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     "Du, Fan" <fan.du@intel.com>
Cc:     "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
        "Wu, Fengguang" <fengguang.wu@intel.com>,
        "Williams, Dan J" <dan.j.williams@intel.com>,
        "Hansen, Dave" <dave.hansen@intel.com>,
        "xishi.qiuxishi@alibaba-inc.com" <xishi.qiuxishi@alibaba-inc.com>,
        "Huang, Ying" <ying.huang@intel.com>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH 5/5] mm, page_alloc: Introduce
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On Thu 25-04-19 08:20:28, Du, Fan wrote:
> 
> 
> >-----Original Message-----
> >From: owner-linux-mm@kvack.org [mailto:owner-linux-mm@kvack.org] On
> >Behalf Of Michal Hocko
> >Sent: Thursday, April 25, 2019 4:10 PM
> >To: Du, Fan <fan.du@intel.com>
> >Cc: akpm@linux-foundation.org; Wu, Fengguang <fengguang.wu@intel.com>;
> >Williams, Dan J <dan.j.williams@intel.com>; Hansen, Dave
> ><dave.hansen@intel.com>; xishi.qiuxishi@alibaba-inc.com; Huang, Ying
> ><ying.huang@intel.com>; linux-mm@kvack.org; linux-kernel@vger.kernel.org
> >Subject: Re: [RFC PATCH 5/5] mm, page_alloc: Introduce
> >ZONELIST_FALLBACK_SAME_TYPE fallback list
> >
> >On Thu 25-04-19 07:55:58, Du, Fan wrote:
> >> >> PMEM is good for frequently read accessed page, e.g. page cache(implicit
> >> >> page
> >> >> request), or user space data base (explicit page request)
> >> >> For now this patch create GFP_SAME_NODE_TYPE for such cases,
> >additional
> >> >> Implementation will be followed up.
> >> >
> >> >Then simply configure that NUMA node as movable and you get these
> >> >allocations for any movable allocation. I am not really convinced a new
> >> >gfp flag is really justified.
> >>
> >> Case 1: frequently write and/or read accessed page deserved to DRAM
> >
> >NUMA balancing
> 
> Sorry, I mean page cache case here.
> Numa balancing works for pages mapped in pagetable style.

I would still expect that a remote PMEM node access latency is
smaller/comparable to the real storage so a promoting part is not that
important for the unmapped pagecache. Maybe I am wrong here but that
really begs for some experiments before we start adding special casing.
-- 
Michal Hocko
SUSE Labs