linux-kernel - Re: [PATCH 1/6] prctl: introduce PR_THP_POLICY_DEFAULT

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Message-ID: <52f12b89-84a1-49ec-a2d2-d710b02218de@redhat.com>
Date: Thu, 15 May 2025 21:20:17 +0200
From: David Hildenbrand <david@...hat.com>
To: "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Usama Arif <usamaarif642@...il.com>,
 Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
 hannes@...xchg.org, shakeel.butt@...ux.dev, riel@...riel.com,
 ziy@...dia.com, laoar.shao@...il.com, baolin.wang@...ux.alibaba.com,
 npache@...hat.com, ryan.roberts@....com, linux-kernel@...r.kernel.org,
 linux-doc@...r.kernel.org, kernel-team@...a.com
Subject: Re: [PATCH 1/6] prctl: introduce PR_THP_POLICY_DEFAULT_HUGE for the
 process

On 15.05.25 20:09, Liam R. Howlett wrote:
> * David Hildenbrand <david@...hat.com> [250515 13:30]:
>>>>
>>>
>>> Did we document all this? :)
>>>
>>> It'd be good to be super explicit about these sorts of 'dependency chains'.
>>>
>>
>> Documentation/admin-guide/mm/transhuge.rst has under "Global THP controls"
>> quite some stuff about all that, yes.
>>
>> The whole document needs an overhaul, to clarify on the whole terminology,
>> make it consistent, and better explain how the pagecache behaves etc. On my
>> todo list, but I'm afraid it will be a bit of work to get it right / please
>> most people.
> 
> Yes, the whole thing is making me grumpy (more than my default state).
> The more I think about it, the more I don't like the prctl approach
> either...
> 
> I more than dislike flags2... I hate it.
> 
> but no prctl, no cgroups, no bpf.. what is left?  A new policy groups
> thing?  No, not that either, please.
> 
> To state the obvious, none of this is transparent.

New to the "transparent" huge page world where not that much is 
"transparent"!?

It's completely in-transparent to most people how it works :D

Yeah, that's why I suggested to piggyback on VM_HUGEPAGE/VM_NOHUGEPAGE. 
Something we already have and that we will probably have for a long time 
... :)

-- 
Cheers,

David / dhildenb