From: Baolin Wang <baolin.wang@linux.alibaba.com>
To: Wei Xu <weixugc@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
Huang Ying <ying.huang@intel.com>,
Dan Williams <dan.j.williams@intel.com>,
Yang Shi <shy828301@gmail.com>, Linux MM <linux-mm@kvack.org>,
Greg Thelen <gthelen@google.com>,
"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
Jagdish Gediya <jvgediya@linux.ibm.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Alistair Popple <apopple@nvidia.com>,
Michal Hocko <mhocko@kernel.org>,
Brice Goglin <brice.goglin@gmail.com>,
Feng Tang <feng.tang@intel.com>,
Jonathan.Cameron@huawei.com
Subject: Re: RFC: Memory Tiering Kernel Interfaces
Date: Tue, 3 May 2022 10:07:08 +0800 [thread overview]
Message-ID: <87f8d4d0-6d06-7254-b2a6-3ccf6a555733@linux.alibaba.com> (raw)
In-Reply-To: <20220501175813.tvytoosygtqlh3nn@offworld>
On 5/2/2022 1:58 AM, Davidlohr Bueso wrote:
> Nice summary, thanks. I don't know who of the interested parties will be
> at lsfmm, but fyi we have a couple of sessions on memory tiering Tuesday
> at 14:00 and 15:00.
>
> On Fri, 29 Apr 2022, Wei Xu wrote:
>
>> The current kernel has the basic memory tiering support: Inactive
>> pages on a higher tier NUMA node can be migrated (demoted) to a lower
>> tier NUMA node to make room for new allocations on the higher tier
>> NUMA node. Frequently accessed pages on a lower tier NUMA node can be
>> migrated (promoted) to a higher tier NUMA node to improve the
>> performance.
>
> Regardless of the promotion algorithm, at some point I see the NUMA hinting
> fault mechanism being in the way of performance. It would be nice if
> hardware
> began giving us page "heatmaps" instead of having to rely on faulting or
> sampling based ways to identify hot memory.
>
>> A tiering relationship between NUMA nodes in the form of demotion path
>> is created during the kernel initialization and updated when a NUMA
>> node is hot-added or hot-removed. The current implementation puts all
>> nodes with CPU into the top tier, and then builds the tiering hierarchy
>> tier-by-tier by establishing the per-node demotion targets based on
>> the distances between nodes.
>>
>> The current memory tiering interface needs to be improved to address
>> several important use cases:
>>
>> * The current tiering initialization code always initializes
>> each memory-only NUMA node into a lower tier. But a memory-only
>> NUMA node may have a high performance memory device (e.g. a DRAM
>> device attached via CXL.mem or a DRAM-backed memory-only node on
>> a virtual machine) and should be put into the top tier.
>
> At least the CXL memory (volatile or not) will still be slower than
> regular DRAM, so I think that we'd not want this to be top-tier. But
> in general, yes I agree that defining top tier as whether or not the
> node has a CPU a bit limiting, as you've detailed here.
>
>> Tiering Hierarchy Initialization
>> ================================
>>
>> By default, all memory nodes are in the top tier (N_TOPTIER_MEMORY).
>>
>> A device driver can remove its memory nodes from the top tier, e.g.
>> a dax driver can remove PMEM nodes from the top tier.
>>
>> The kernel builds the memory tiering hierarchy and per-node demotion
>> order tier-by-tier starting from N_TOPTIER_MEMORY. For a node N, the
>> best distance nodes in the next lower tier are assigned to
>> node_demotion[N].preferred and all the nodes in the next lower tier
>> are assigned to node_demotion[N].allowed.
>>
>> node_demotion[N].preferred can be empty if no preferred demotion node
>> is available for node N.
>
> Upon cases where there more than one possible demotion node (with equal
> cost), I'm wondering if we want to do something better than choosing
> randomly, like we do now - perhaps round robin? Of course anything
> like this will require actual performance data, something I have seen
> very little of.
I've tried to use round robin[1] to select a target demotion node if
there are multiple demotion nodes, however I did not see any obvious
performance gain with mysql testing. Maybe use other test suits?
https://lore.kernel.org/all/c02bcbc04faa7a2c852534e9cd58a91c44494657.1636016609.git.baolin.wang@linux.alibaba.com/
next prev parent reply other threads:[~2022-05-03 2:06 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-30 2:10 RFC: Memory Tiering Kernel Interfaces Wei Xu
2022-04-30 3:59 ` Yang Shi
2022-04-30 6:37 ` Wei Xu
2022-05-06 0:01 ` Alistair Popple
2022-05-10 4:32 ` Wei Xu
2022-05-10 5:37 ` Alistair Popple
2022-05-10 11:38 ` Aneesh Kumar K.V
2022-05-11 5:30 ` Wei Xu
2022-05-11 7:34 ` Alistair Popple
2022-05-11 7:49 ` ying.huang
2022-05-11 17:07 ` Wei Xu
2022-05-12 1:42 ` ying.huang
2022-05-12 2:39 ` Wei Xu
2022-05-12 3:13 ` ying.huang
2022-05-12 3:37 ` Wei Xu
2022-05-12 6:24 ` Wei Xu
2022-05-06 18:56 ` Yang Shi
2022-05-09 14:32 ` Hesham Almatary
2022-05-10 3:24 ` Yang Shi
2022-05-10 9:59 ` Hesham Almatary
2022-05-10 12:10 ` Aneesh Kumar K V
2022-05-11 5:42 ` Wei Xu
2022-05-11 7:12 ` Alistair Popple
2022-05-11 9:05 ` Hesham Almatary
2022-05-12 3:02 ` ying.huang
2022-05-12 4:40 ` Aneesh Kumar K V
2022-05-12 4:49 ` Wei Xu
2022-05-10 4:22 ` Wei Xu
2022-05-10 10:01 ` Hesham Almatary
2022-05-10 11:44 ` Aneesh Kumar K.V
2022-05-01 18:35 ` Dan Williams
2022-05-03 6:36 ` Wei Xu
2022-05-06 19:05 ` Yang Shi
2022-05-07 7:56 ` ying.huang
2022-05-01 17:58 ` Davidlohr Bueso
2022-05-02 1:04 ` David Rientjes
2022-05-02 7:23 ` Aneesh Kumar K.V
2022-05-03 2:07 ` Baolin Wang [this message]
2022-05-03 6:06 ` Wei Xu
2022-05-03 17:14 ` Alistair Popple
2022-05-03 17:47 ` Dave Hansen
2022-05-03 22:35 ` Alistair Popple
2022-05-03 23:54 ` Dave Hansen
2022-05-04 1:31 ` Wei Xu
2022-05-04 17:02 ` Dave Hansen
2022-05-05 6:35 ` Wei Xu
2022-05-05 14:24 ` Dave Hansen
2022-05-10 4:43 ` Wei Xu
2022-05-02 6:25 ` Aneesh Kumar K.V
2022-05-03 7:02 ` Wei Xu
2022-05-02 15:20 ` Dave Hansen
2022-05-03 7:19 ` Wei Xu
2022-05-03 19:12 ` Tim Chen
2022-05-05 7:02 ` Wei Xu
2022-05-05 8:57 ` ying.huang
2022-05-05 23:57 ` Alistair Popple
2022-05-06 0:25 ` Alistair Popple
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