linux-kernel - Re: [RFC PATCH] mm: control mthp per process/cgroup

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Message-ID: <15f31ce4-6e41-4444-963b-77c9bea33b86@redhat.com>
Date: Mon, 2 Sep 2024 15:33:11 +0200
From: David Hildenbrand <david@...hat.com>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>,
 Nanyong Sun <sunnanyong@...wei.com>, Matthew Wilcox <willy@...radead.org>
Cc: hughd@...gle.com, akpm@...ux-foundation.org, ryan.roberts@....com,
 baohua@...nel.org, ioworker0@...il.com, peterx@...hat.com, ziy@...dia.com,
 wangkefeng.wang@...wei.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] mm: control mthp per process/cgroup

On 02.09.24 11:36, Baolin Wang wrote:
> 
> 
> On 2024/8/19 13:58, Nanyong Sun wrote:
>> On 2024/8/17 2:15, Matthew Wilcox wrote:
>>
>>> On Fri, Aug 16, 2024 at 05:13:27PM +0800, Nanyong Sun wrote:
>>>> Now the large folio control interfaces is system wide and tend to be
>>>> default on: file systems use large folio by default if supported,
>>>> mTHP is tend to default enable when boot [1].
>>>> When large folio enabled, some workloads have performance benefit,
>>>> but some may not and some side effects can happen: the memory usage
>>>> may increase, direct reclaim maybe more frequently because of more
>>>> large order allocations, result in cpu usage also increases. We observed
>>>> this on a product environment which run nginx, the pgscan_direct count
>>>> increased a lot than before, can reach to 3000 times per second, and
>>>> disable file large folio can fix this.
>>> Can you share any details of your nginx workload that shows a regression?
>>> The heuristics for allocating large folios are completely untuned, so
>>> having data for a workload which performs better with small folios is
>>> very valuable.
>>>
>>> .
>> The RPS(/Requests per second/) which is the performance metric of nginx
>> workload has no
>> regression(also no improvement)，we just observed that  pgscan_direct
>> rate is much higher
>> with large folio.
>> So far, we have tested some workloads' benchmark, some did not have
>> performance improvement
>> but also did not have regression.
>> In a production environment, different workloads may be deployed on a
>> machine. Therefore,
>> do we need to add a process/cgroup level control to prevent workloads
>> that will not have
>> performance improvement from using mTHP? In this way, the memory
>> overhead and direct reclaim
>> caused by mTHP can be avoided for those process/cgroup.
> 
> OK. So no regression with mTHP, seems just some theoretical analysis.
> 
> IMHO, it would be better to evaluate your 'per-cgroup mTHP control' idea
> on some real workloads, and gather some data to evaluation, which can be
> more convincing.

Agreed!

-- 
Cheers,

David / dhildenb