linux-kernel - Re: [PATCH v4 7/7] selftests: prctl: introduce tests for disabling THPs except for madvise

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Message-ID: <620a586e-54a2-4ce0-9cf7-2ddf4b6ef59d@sirena.org.uk>
Date: Thu, 14 Aug 2025 14:08:57 +0100
From: Mark Brown <broonie@...nel.org>
To: David Hildenbrand <david@...hat.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Usama Arif <usamaarif642@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org, corbet@....net, rppt@...nel.org,
	surenb@...gle.com, mhocko@...e.com, hannes@...xchg.org,
	baohua@...nel.org, shakeel.butt@...ux.dev, riel@...riel.com,
	ziy@...dia.com, laoar.shao@...il.com, dev.jain@....com,
	baolin.wang@...ux.alibaba.com, npache@...hat.com,
	Liam.Howlett@...cle.com, ryan.roberts@....com, vbabka@...e.cz,
	jannh@...gle.com, Arnd Bergmann <arnd@...db.de>, sj@...nel.org,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	kernel-team@...a.com
Subject: Re: [PATCH v4 7/7] selftests: prctl: introduce tests for disabling
 THPs except for madvise

On Thu, Aug 14, 2025 at 02:59:13PM +0200, David Hildenbrand wrote:
> On 14.08.25 14:09, Mark Brown wrote:

> > Perhaps this is something that needs considering in the ABI, so
> > userspace can reasonably figure out if it failed to configure whatever
> > is being configured due to a missing feature (in which case it should
> > fall back to not using that feature somehow) or due to it messing
> > something else up?  We might be happy with the tests being version
> > specific but general userspace should be able to be a bit more robust.

> Yeah, the whole prctl() ship has sailed, unfortunately :(

Perhaps a second call or sysfs file or something that returns the
supported mask?  You'd still have a boostrapping issue with existing
versions but at least at any newer stuff would be helped.

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