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SubjectRE: [RFC PATCH 5/5] mm, page_alloc: Introduce ZONELIST_FALLBACK_SAME_TYPE fallback list
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>-----Original Message-----
>From: owner-linux-mm@kvack.org [mailto:owner-linux-mm@kvack.org] On
>Behalf Of Michal Hocko
>Sent: Thursday, April 25, 2019 3:49 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 07:43:09, Du, Fan wrote:
>>
>>
>> >-----Original Message-----
>> >From: Michal Hocko [mailto:mhocko@kernel.org]
>> >Sent: Thursday, April 25, 2019 2:38 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 09:21:35, Fan Du wrote:
>> >> On system with heterogeneous memory, reasonable fall back lists woul
>be:
>> >> a. No fall back, stick to current running node.
>> >> b. Fall back to other nodes of the same type or different type
>> >> e.g. DRAM node 0 -> DRAM node 1 -> PMEM node 2 -> PMEM node
>3
>> >> c. Fall back to other nodes of the same type only.
>> >> e.g. DRAM node 0 -> DRAM node 1
>> >>
>> >> a. is already in place, previous patch implement b. providing way to
>> >> satisfy memory request as best effort by default. And this patch of
>> >> writing build c. to fallback to the same node type when user specify
>> >> GFP_SAME_NODE_TYPE only.
>> >
>> >So an immediate question which should be answered by this changelog.
>Who
>> >is going to use the new gfp flag? Why cannot all allocations without an
>> >explicit numa policy fallback to all existing nodes?
>>
>> 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
Case 2: frequently read accessed page deserved to PMEM

We need something like a new gfp flag to sort above two cases out
From each other.

>--
>Michal Hocko
>SUSE Labs

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