linux-kernel - Re: [RFC PATCH V4 1/1] mm: add last level page table numa info to /proc/pid/numa

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Date:   Thu, 4 Aug 2022 17:30:33 +0800
From:   haoxin <xhao@...ux.alibaba.com>
To:     David Hildenbrand <david@...hat.com>, willy@...radead.org
Cc:     akpm@...ux-foundation.org, adobriyan@...il.com,
        keescook@...omium.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [RFC PATCH V4 1/1] mm: add last level page table numa info to
 /proc/pid/numa_pgtable


在 2022/8/4 下午4:12, David Hildenbrand 写道:
> On 04.08.22 10:04, haoxin wrote:
>> 在 2022/8/1 下午9:28, David Hildenbrand 写道:
>>> On 01.08.22 14:17, Xin Hao wrote:
>>>> In many data center servers, the shared memory architectures is
>>>> Non-Uniform Memory Access (NUMA), remote numa node data access
>>>> often brings a high latency problem, but what we are easy to ignore
>>>> is that the page table remote numa access, It can also leads to a
>>>> performance degradation.
>>> Let me try rewriting:
>>>
>>> "
>>> Many data center servers employ Non-Uniform Memory Access (NUMA)
>>> architectures. Remote numa memory access results in high latency. While
>>> memory placement is one issue, sub-optimal page table placement can also
>>> result in surprise performance degradation.
>>> "
>> Thanks,  it reads more clearly.
>>
>>>> So there add a new interface in /proc, This will help developers to
>>>> get more info about performance issues if they are caused by cross-NUMA.
>>> Why do we only care about "last level page table", why not about the others?
>>>
>>> IMHO, we could emit something like "0, 1, 3, 0" instead for a given user
>>> space address, showing the NUMA node the page table belongs to from
>>> highest to lowest page table level.
>> I have planned to implement the PTE page table in this version first,
>> and then support other page tables in the next patch later.
> If there are plans, let's do it all at once, to get a good and single
> interface to expose that information.
Ok, thanks for your suggestion, I will implement it in the next version.

>