linux-kernel - Re: [RFC][PATCH v2 10/21] mm: build separate zonelist for PMEM and DRAM node

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Message-Id: <87h8ekk19s.fsf@linux.ibm.com>
Date:   Mon, 07 Jan 2019 19:39:19 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
To:     Fengguang Wu <fengguang.wu@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Fan Du <fan.du@...el.com>, kvm@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Yao Yuan <yuan.yao@...el.com>,
        Peng Dong <dongx.peng@...el.com>,
        Huang Ying <ying.huang@...el.com>,
        Liu Jingqi <jingqi.liu@...el.com>,
        Dong Eddie <eddie.dong@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Zhang Yi <yi.z.zhang@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [RFC][PATCH v2 10/21] mm: build separate zonelist for PMEM and DRAM node

Fengguang Wu <fengguang.wu@...el.com> writes:

> On Tue, Jan 01, 2019 at 02:44:41PM +0530, Aneesh Kumar K.V wrote:
>>Fengguang Wu <fengguang.wu@...el.com> writes:
>>
>>> From: Fan Du <fan.du@...el.com>
>>>
>>> When allocate page, DRAM and PMEM node should better not fall back to
>>> each other. This allows migration code to explicitly control which type
>>> of node to allocate pages from.
>>>
>>> With this patch, PMEM NUMA node can only be used in 2 ways:
>>> - migrate in and out
>>> - numactl
>>
>>Can we achieve this using nodemask? That way we don't tag nodes with
>>different properties such as DRAM/PMEM. We can then give the
>>flexibilility to the device init code to add the new memory nodes to
>>the right nodemask
>
> Aneesh, in patch 2 we did create nodemask numa_nodes_pmem and
> numa_nodes_dram. What's your supposed way of "using nodemask"?
>

IIUC the patch is to avoid allocation from PMEM nodes and the way you
achieve it is by checking if (is_node_pmem(n)). We already have
abstractness to avoid allocation from a node using node mask. I was
wondering whether we can do the equivalent of above using that.

ie, __next_zone_zonelist can do zref_in_nodemask(z,
default_exclude_nodemask)) and decide whether to use the specific zone
or not.

That way we don't add special code like 

+	PGDAT_DRAM,			/* Volatile DRAM memory node */
+	PGDAT_PMEM,			/* Persistent memory node */

The reason is that there could be other device memory that would want to
get excluded from that default allocation like you are doing for PMEM

-aneesh