From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
To: "ying.huang@intel.com" <ying.huang@intel.com>,
Jagdish Gediya <jvgediya@linux.ibm.com>,
Wei Xu <weixugc@google.com>, Yang Shi <shy828301@gmail.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Dan Williams <dan.j.williams@intel.com>,
Davidlohr Bueso <dave@stgolabs.net>
Cc: Linux MM <linux-mm@kvack.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Baolin Wang <baolin.wang@linux.alibaba.com>,
Greg Thelen <gthelen@google.com>, MichalHocko <mhocko@kernel.org>,
Brice Goglin <brice.goglin@gmail.com>
Subject: Re: [PATCH v2 0/5] mm: demotion: Introduce new node state N_DEMOTION_TARGETS
Date: Mon, 25 Apr 2022 09:20:14 +0530 [thread overview]
Message-ID: <8735i1zurt.fsf@linux.ibm.com> (raw)
In-Reply-To: <200e95cf36c1642512d99431014db8943fed715d.camel@intel.com>
"ying.huang@intel.com" <ying.huang@intel.com> writes:
> Hi, All,
>
> On Fri, 2022-04-22 at 16:30 +0530, Jagdish Gediya wrote:
>
> [snip]
>
>> I think it is necessary to either have per node demotion targets
>> configuration or the user space interface supported by this patch
>> series. As we don't have clear consensus on how the user interface
>> should look like, we can defer the per node demotion target set
>> interface to future until the real need arises.
>>
>> Current patch series sets N_DEMOTION_TARGET from dax device kmem
>> driver, it may be possible that some memory node desired as demotion
>> target is not detected in the system from dax-device kmem probe path.
>>
>> It is also possible that some of the dax-devices are not preferred as
>> demotion target e.g. HBM, for such devices, node shouldn't be set to
>> N_DEMOTION_TARGETS. In future, Support should be added to distinguish
>> such dax-devices and not mark them as N_DEMOTION_TARGETS from the
>> kernel, but for now this user space interface will be useful to avoid
>> such devices as demotion targets.
>>
>> We can add read only interface to view per node demotion targets
>> from /sys/devices/system/node/nodeX/demotion_targets, remove
>> duplicated /sys/kernel/mm/numa/demotion_target interface and instead
>> make /sys/devices/system/node/demotion_targets writable.
>>
>> Huang, Wei, Yang,
>> What do you suggest?
>
> We cannot remove a kernel ABI in practice. So we need to make it right
> at the first time. Let's try to collect some information for the kernel
> ABI definitation.
>
> The below is just a starting point, please add your requirements.
>
> 1. Jagdish has some machines with DRAM only NUMA nodes, but they don't
> want to use that as the demotion targets. But I don't think this is a
> issue in practice for now, because demote-in-reclaim is disabled by
> default.
It is not just that the demotion can be disabled. We should be able to
use demotion on a system where we can find DRAM only NUMA nodes. That
cannot be achieved by /sys/kernel/mm/numa/demotion_enabled. It needs
something similar to to N_DEMOTION_TARGETS
>
> 2. For machines with PMEM installed in only 1 of 2 sockets, for example,
>
> Node 0 & 2 are cpu + dram nodes and node 1 are slow
> memory node near node 0,
>
> available: 3 nodes (0-2)
> node 0 cpus: 0 1
> node 0 size: n MB
> node 0 free: n MB
> node 1 cpus:
> node 1 size: n MB
> node 1 free: n MB
> node 2 cpus: 2 3
> node 2 size: n MB
> node 2 free: n MB
> node distances:
> node 0 1 2
> 0: 10 40 20
> 1: 40 10 80
> 2: 20 80 10
>
> We have 2 choices,
>
> a)
> node demotion targets
> 0 1
> 2 1
This is achieved by
[PATCH v2 1/5] mm: demotion: Set demotion list differently
>
> b)
> node demotion targets
> 0 1
> 2 X
>
> a) is good to take advantage of PMEM. b) is good to reduce cross-socket
> traffic. Both are OK as defualt configuration. But some users may
> prefer the other one. So we need a user space ABI to override the
> default configuration.
>
> 3. For machines with HBM (High Bandwidth Memory), as in
>
> https://lore.kernel.org/lkml/39cbe02a-d309-443d-54c9-678a0799342d@gmail.com/
>
>> [1] local DDR = 10, remote DDR = 20, local HBM = 31, remote HBM = 41
>
> Although HBM has better performance than DDR, in ACPI SLIT, their
> distance to CPU is longer. We need to provide a way to fix this. The
> user space ABI is one way. The desired result will be to use local DDR
> as demotion targets of local HBM.
IMHO the above (2b and 3) can be done using per node demotion targets. Below is
what I think we could do with a single slow memory NUMA node 4.
/sys/devices/system/node# cat node[0-4]/demotion_targets
4
4
4
4
/sys/devices/system/node# echo 1 > node1/demotion_targets
bash: echo: write error: Invalid argument
/sys/devices/system/node# cat node[0-4]/demotion_targets
4
4
4
4
/sys/devices/system/node# echo 0 > node1/demotion_targets
/sys/devices/system/node# cat node[0-4]/demotion_targets
4
0
4
4
/sys/devices/system/node# echo 1 > node0/demotion_targets
bash: echo: write error: Invalid argument
/sys/devices/system/node# cat node[0-4]/demotion_targets
4
0
4
4
Disable demotion for a specific node.
/sys/devices/system/node# echo > node1/demotion_targets
/sys/devices/system/node# cat node[0-4]/demotion_targets
4
4
4
Reset demotion to default
/sys/devices/system/node# echo -1 > node1/demotion_targets
/sys/devices/system/node# cat node[0-4]/demotion_targets
4
4
4
4
When a specific device/NUMA node is used for demotion target via the user interface, it is taken
out of other NUMA node targets.
root@ubuntu-guest:/sys/devices/system/node# cat node[0-4]/demotion_targets
4
4
4
4
/sys/devices/system/node# echo 4 > node1/demotion_targets
/sys/devices/system/node# cat node[0-4]/demotion_targets
4
If more than one node requies the same demotion target
/sys/devices/system/node# echo 4 > node0/demotion_targets
/sys/devices/system/node# cat node[0-4]/demotion_targets
4
4
-aneesh
next prev parent reply other threads:[~2022-04-25 3:50 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-13 9:22 [PATCH v2 0/5] mm: demotion: Introduce new node state N_DEMOTION_TARGETS Jagdish Gediya
2022-04-13 9:22 ` [PATCH v2 1/5] mm: demotion: Set demotion list differently Jagdish Gediya
2022-04-14 7:09 ` ying.huang
2022-04-14 8:48 ` Jagdish Gediya
2022-04-14 8:57 ` ying.huang
2022-04-14 8:55 ` Baolin Wang
2022-04-14 9:02 ` Jonathan Cameron
2022-04-14 10:40 ` Jagdish Gediya
2022-04-21 6:13 ` ying.huang
2022-04-13 9:22 ` [PATCH v2 2/5] mm: demotion: Add new node state N_DEMOTION_TARGETS Jagdish Gediya
2022-04-21 4:33 ` Wei Xu
2022-04-13 9:22 ` [PATCH v2 3/5] mm: demotion: Add support to set targets from userspace Jagdish Gediya
2022-04-21 4:26 ` Wei Xu
2022-04-22 9:13 ` Jagdish Gediya
2022-04-21 5:31 ` Wei Xu
2022-04-13 9:22 ` [PATCH v2 4/5] device-dax/kmem: Set node state as N_DEMOTION_TARGETS Jagdish Gediya
2022-04-13 9:22 ` [PATCH v2 5/5] mm: demotion: Build demotion list based on N_DEMOTION_TARGETS Jagdish Gediya
2022-04-13 21:44 ` [PATCH v2 0/5] mm: demotion: Introduce new node state N_DEMOTION_TARGETS Andrew Morton
2022-04-14 10:16 ` Jagdish Gediya
2022-04-14 7:00 ` ying.huang
2022-04-14 10:19 ` Jagdish Gediya
2022-04-21 3:11 ` Yang Shi
2022-04-21 5:41 ` Wei Xu
2022-04-21 6:24 ` ying.huang
2022-04-21 6:49 ` Wei Xu
2022-04-21 7:08 ` ying.huang
2022-04-21 7:29 ` Wei Xu
2022-04-21 7:45 ` ying.huang
2022-04-21 18:26 ` Wei Xu
2022-04-22 0:58 ` ying.huang
2022-04-22 4:46 ` Wei Xu
2022-04-22 5:40 ` ying.huang
2022-04-22 6:13 ` Wei Xu
2022-04-22 6:21 ` ying.huang
2022-04-22 11:00 ` Jagdish Gediya
2022-04-22 16:43 ` Wei Xu
2022-04-22 17:29 ` Yang Shi
2022-04-24 3:02 ` ying.huang
2022-04-25 3:50 ` Aneesh Kumar K.V [this message]
2022-04-25 6:10 ` ying.huang
2022-04-25 8:09 ` Aneesh Kumar K V
2022-04-25 8:54 ` Aneesh Kumar K V
2022-04-25 20:17 ` Davidlohr Bueso
2022-04-26 8:42 ` ying.huang
2022-04-26 9:02 ` Aneesh Kumar K V
2022-04-26 9:44 ` ying.huang
2022-04-27 4:27 ` Wei Xu
2022-04-25 7:26 ` Jagdish Gediya
2022-04-25 16:56 ` Wei Xu
2022-04-27 5:06 ` Aneesh Kumar K V
2022-04-27 18:27 ` Wei Xu
2022-04-28 0:56 ` ying.huang
2022-04-28 4:11 ` Wei Xu
2022-04-28 17:14 ` Yang Shi
2022-04-29 1:27 ` Alistair Popple
2022-04-29 2:21 ` ying.huang
2022-04-29 2:58 ` Wei Xu
2022-04-29 3:27 ` ying.huang
2022-04-29 4:45 ` Alistair Popple
2022-04-29 18:53 ` Yang Shi
2022-04-29 18:52 ` Yang Shi
2022-04-27 7:11 ` ying.huang
2022-04-27 16:27 ` Wei Xu
2022-04-28 8:37 ` ying.huang
[not found] ` <DM6PR11MB4107867291AFE0C210D9052ADCFD9@DM6PR11MB4107.namprd11.prod.outlook.com>
2022-04-30 2:21 ` Wei Xu
2022-04-21 17:56 ` Yang Shi
2022-04-21 23:48 ` ying.huang
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