linux-kernel - Re: [PATCH v4] mm/demotion: Expose memory tier details via sysfs

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Date:   Mon, 26 Sep 2022 09:04:16 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Aneesh Kumar K V <aneesh.kumar@...ux.ibm.com>
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org,
        Wei Xu <weixugc@...gle.com>, Yang Shi <shy828301@...il.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Tim C Chen <tim.c.chen@...el.com>,
        Michal Hocko <mhocko@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Hesham Almatary <hesham.almatary@...wei.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Alistair Popple <apopple@...dia.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Johannes Weiner <hannes@...xchg.org>, jvgediya.oss@...il.com,
        Bharata B Rao <bharata@....com>
Subject: Re: [PATCH v4] mm/demotion: Expose memory tier details via sysfs

Aneesh Kumar K V <aneesh.kumar@...ux.ibm.com> writes:

> On 9/23/22 1:37 PM, Huang, Ying wrote:
>> "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com> writes:
>> 
>>> This patch adds /sys/devices/virtual/memory_tiering/ where all memory tier
>>> related details can be found. All allocated memory tiers will be listed
>>> there as /sys/devices/virtual/memory_tiering/memory_tierN/
>>>
>>> The nodes which are part of a specific memory tier can be listed via
>>> /sys/devices/virtual/memory_tiering/memory_tierN/nodes
>> 
>> It appears that XXXs is used for mask while XXXs_list is used for list?
>> For example,
>> 
>> # cat /sys/devices/system/cpu/cpu2/topology/core_cpus
>> 0,00100004
>> # cat /sys/devices/system/cpu/cpu2/topology/core_cpus_list
>> 2,20
>> 
>> It's better to follow the this convention?
>> 
>
> That is not followed in other parts of the kernel. I was loking at cpuset 
>
> $cat cpuset.cpus.effective 
> 0-7

Per my understanding, cpuset isn't sysfs, but cgroupfs?

I did some research in my system,

$ grep . $(find /sys/devices | grep 'list$')

and

$ grep . $(find /sys/devices | grep 'cpus$')

I found that the cpus/cpus_list convention is used in

- pci

  /sys/devices/pci0000:64/0000:64:0d.2/local_cpulist:0-35
  /sys/devices/pci0000:64/0000:64:0c.2/local_cpus:f,ffffffff

- system

  /sys/devices/system/cpu/cpu7/topology/core_cpus_list:7,25
  /sys/devices/system/cpu/cpu7/topology/core_cpus:0,02000080

- block

  /sys/devices/virtual/block/loop1/mq/0/cpu_list:0, 1, 2, ...

- net

  /sys/devices/virtual/net/lo/queues/rx-0/rps_cpus:0,00000000

And I haven't found any exception in sysfs of my system.  Can you find
some?

Best Regards,
Huang, Ying

>>> A directory hierarchy looks like
>>> :/sys/devices/virtual/memory_tiering$ tree memory_tier4/
>>> memory_tier4/
>>> ├── nodes
>>> ├── subsystem -> ../../../../bus/memory_tiering
>>> └── uevent
>>>
>>> :/sys/devices/virtual/memory_tiering$ cat memory_tier4/nodes
>>> 0,2
>>>
>>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
>> 
>> Best Regards,
>> Huang, Ying
>> 
>> [snip]