From: Davidlohr Bueso <dave@stgolabs.net>
To: Aneesh Kumar K V <aneesh.kumar@linux.ibm.com>
Cc: "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>,
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 13:17:28 -0700 [thread overview]
Message-ID: <20220425201728.5kzm4seu7rep7ndr@offworld> (raw)
In-Reply-To: <c576a992-5a50-5dd3-644c-a45d4338fc85@linux.ibm.com>
On Mon, 25 Apr 2022, Aneesh Kumar K V wrote:
>On 4/25/22 11:40 AM, ying.huang@intel.com wrote:
>>On Mon, 2022-04-25 at 09:20 +0530, Aneesh Kumar K.V wrote:
>>>"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
>>>
>>
>>Can you show NUMA information of your machines with DRAM-only nodes and
>>PMEM nodes? We can try to find the proper demotion order for the
>>system. If you can not show it, we can defer N_DEMOTION_TARGETS until
>>the machine is available.
>
>
>Sure will find one such config. As you might have noticed this is very
>easy to have in a virtualization setup because the hypervisor can
>assign memory to a guest VM from a numa node that doesn't have CPU
>assigned to the same guest. This depends on the other guest VM
>instance config running on the system. So on any virtualization config
>that has got persistent memory attached, this can become an easy
>config to end up with.
And as hw becomes available things like CXL will also start to show
"interesting" setups. You have a mix of volatile and/or pmem nodes
with different access costs, so: CPU+DRAM, DRAM (?), volatile CXL mem,
CXL pmem, non-cxl pmem.
imo, by default, slower mem should be demotion candidates regardless of
type or socket layout (which can be a last consideration such that this
is somewhat mitigated). And afaict this is along the lines of what Jagdish's
first example refers to in patch 1/5.
>
>>>>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
Yes, I think it makes sense to do 2a.
Thanks,
Davidlohr
next prev parent reply other threads:[~2022-04-25 20:17 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
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 [this message]
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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