linux-kernel - Re: [PATCH v4 0/2] fix MADV_COLLAPSE issue if THP settings are disabled

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <6bda0de6-1ade-40c9-aa52-16bc02d98bee@redhat.com>
Date: Wed, 25 Jun 2025 09:49:48 +0200
From: David Hildenbrand <david@...hat.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Hugh Dickins <hughd@...gle.com>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>, akpm@...ux-foundation.org,
 ziy@...dia.com, Liam.Howlett@...cle.com, npache@...hat.com,
 ryan.roberts@....com, dev.jain@....com, baohua@...nel.org,
 zokeefe@...gle.com, shy828301@...il.com, usamaarif642@...il.com,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 0/2] fix MADV_COLLAPSE issue if THP settings are
 disabled

On 25.06.25 09:42, Lorenzo Stoakes wrote:
> On Wed, Jun 25, 2025 at 09:36:53AM +0200, David Hildenbrand wrote:
>> On 25.06.25 09:30, Lorenzo Stoakes wrote:
>>> I _guarantee_ you that's what nearly everybody except a handful of people will
>>> expect.
>>
>> I know, See my other mail, the problem is rather if there is no somebody
>> relying on never+MADV_COLLAPSE from doing the MADV_COLLAPSE-documented
>> thing.
>>
>> It's a mess.
> 
> Well now we have an almost philosophical debate - we have different sets of
> users, 99% of whom believe the uAPI is X, and 1% of whom believe it is Y.
> 
> Now what is the uAPI? What is 'breaking userspace'? :)

Yeah, that's why I mentioned that I think we broke "something" when we 
changed the semantics. But that breakage probably only affects real 
corner cases (debugging, customer workarounds).

I think the whole use case of using MADV_COLLAPSE to completely control 
THP allocation in a system is otherwise pretty hard to achieve, if there 
is no other way to tame THP allocation through page faults+khugepaged.

Mess.

-- 
Cheers,

David / dhildenb