linux-kernel - Re: [DISCUSSION] proposed mctl() API

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: <12d7db2e-3a2c-47a2-a973-4110d2424c71@lucifer.local>
Date: Wed, 4 Jun 2025 13:28:45 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        Shakeel Butt <shakeel.butt@...ux.dev>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        David Hildenbrand <david@...hat.com>, Vlastimil Babka <vbabka@...e.cz>,
        Jann Horn <jannh@...gle.com>, Arnd Bergmann <arnd@...db.de>,
        Christian Brauner <brauner@...nel.org>, SeongJae Park <sj@...nel.org>,
        Usama Arif <usamaarif642@...il.com>, Mike Rapoport <rppt@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>, Barry Song <21cnbao@...il.com>,
        linux-mm@...ck.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        Pedro Falcato <pfalcato@...e.de>
Subject: Re: [DISCUSSION] proposed mctl() API

On Thu, May 29, 2025 at 04:28:46PM +0100, Matthew Wilcox wrote:
> On Thu, May 29, 2025 at 03:43:26PM +0100, Lorenzo Stoakes wrote:
> > After discussions in various threads (Usama's series adding a new prctl()
> > in [0], and a proposal to adapt process_madvise() to do the same -
> > conception in [1] and RFC in [2]), it seems fairly clear that it would make
> > sense to explore a dedicated API to explicitly allow for actions which
> > affect the virtual address space as a whole.
> >
> > Also, Barry is implementing a feature (currently under RFC) which could
> > additionally make use of this API (see [3]).
>
> I think the reason that you're having trouble coming up with a good
> place to put these ideas is because they are all bad ideas.  Do none of
> them.  Problem solved.
>
> People should put more effort into allocating THPs automatically and
> monitoring where they're helping performance and where they're hurting
> performance, instead of coming up with these baroque reasons to blame
> the sysadmin for not having tweaked some magic knob.
>
> Barry's problem is that we're all nervous about possibly regressing
> performance on some unknown workloads.  Just try Barry's proposal, see
> if anyone actually compains or if we're just afraid of our own shadows.
>

So from my perspective - I very much agree with the concept of doing nothing
here, ideally :)

But I feel we need to look at this problem from both the short term and the
long term - in the long run I absolutely agree with what you say.

In the short term this proposal is broadly 'what is the least worst means
of establishing policy like this?'.

I think there is broad agreement that prctl() is sub-optimal, so an
mm-specific API makes sense.

So it comes down to a question of - how badly do we need to be able to do
this _now_?