From: David Hildenbrand <david@redhat.com>
To: Liu Song <liusong@linux.alibaba.com>,
Yuanhe Shu <xiangzao@linux.alibaba.com>,
akpm@linux-foundation.org
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm, thp: display [never] for defrag when THP is set to never
Date: Mon, 26 Feb 2024 12:49:51 +0100 [thread overview]
Message-ID: <b44572f7-4aa9-45b4-94bd-6860bebec0cf@redhat.com> (raw)
In-Reply-To: <b1988f61-e68d-4268-911b-8352fb49ea15@redhat.com>
On 26.02.24 12:48, David Hildenbrand wrote:
> On 26.02.24 12:22, Liu Song wrote:
>>
>> 在 2024/2/26 16:54, David Hildenbrand 写道:
>>> On 23.02.24 12:01, Liu Song wrote:
>>>>
>>>> 在 2024/2/22 20:14, David Hildenbrand 写道:
>>>>> On 22.02.24 12:53, Yuanhe Shu wrote:
>>>>>> When transparent_hugepage is set to never by cmdline or echo, defrag
>>>>>> still show what it used to be and can be modified which makes user
>>>>>> confusing whether defrag would take effect.
>>>>>>
>>>>>> Actually if transparent_hugepage is set to never, defrag will not take
>>>>>> effect. Just Display never and remain unchangeable to for defrag when
>>>>>> transparent_hugepage is set to never.
>>>>>>
>>>>>> Suggested-by: Liu Song <liusong@linux.alibaba.com>
>>>>>> Signed-off-by: Yuanhe Shu <xiangzao@linux.alibaba.com>
>>>>>> ---
>>>>>
>>>>> No, I don't think we want such a dependency between both options.
>>>>>
>>>>> You might just end up breaking existing scripts (enable defrag before
>>>>> enabling THP) for no good reason.
>>>>>
>>>> In certain situations where khugepaged_thread is NULL, it would be more
>>>> reasonable for the value of
>>>> /sys/kernel/mm/transparent_hugepage/khugepaged/defrag to be 0. The patch
>>>> should include a fix for this case.
>>>
>>> Why?
>>>
>>> We have a bunch of THP toggles. They reside in
>>> "/sys/kernel/mm/transparent_hugepage/", indicating that they are THP
>>> specific.
>>>
>>> Some of them are only in effect if some other toggles are set.
>>>
>>> That is very common practice.
>>>
>>> If you think something could be confusing, maybe clarify the doc? I
>>> don't immediately see why any code changes are required, really.
>>
>> We should explain this in the documentation, but to be honest, many
>> people don't read the documentation, and even after we explicitly
>> disable THP with transparent_hugepage=never, khugepaged/defrag is still
>> set to 1, and users come asking why it's still defragging. We can't
>> expect all users to have technical expertise, or to diligently read
>> through the documentation; it would obviously be best if we could avoid
>> user confusion altogether.
>
> Then tell your users if a feature is enabled
s/enabled/disabled/
s/1on1/101/
Time for a break :D
Anyhow, there has to be a pretty good reason to change the semantics of
these toggles that have been around forever. "users could be confused"
is a not sufficient.
--
Cheers,
David / dhildenb
prev parent reply other threads:[~2024-02-26 11:49 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-22 11:53 [PATCH] mm, thp: display [never] for defrag when THP is set to never Yuanhe Shu
2024-02-22 12:14 ` David Hildenbrand
2024-02-23 11:01 ` Liu Song
2024-02-26 8:54 ` David Hildenbrand
2024-02-26 11:22 ` Liu Song
2024-02-26 11:48 ` David Hildenbrand
2024-02-26 11:49 ` David Hildenbrand [this message]
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