linux-kernel - Re: [PATCH] mm: shmem/tmpfs hugepage defaults config choice

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Message-ID: <aP-JFqlCE6ee5_Ln@shell.ilvokhin.com>
Date: Mon, 27 Oct 2025 15:00:38 +0000
From: Dmitry Ilvokhin <d@...okhin.com>
To: Pedro Falcato <pfalcato@...e.de>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <david@...hat.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>, Hugh Dickins <hughd@...gle.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	Kiryl Shutsemau <kas@...nel.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, kernel-team@...a.com
Subject: Re: [PATCH] mm: shmem/tmpfs hugepage defaults config choice

On Fri, Oct 24, 2025 at 09:27:39PM +0100, Pedro Falcato wrote:
> On Thu, Oct 23, 2025 at 06:12:02PM +0000, Dmitry Ilvokhin wrote:
> > Allow to override defaults for shemem and tmpfs at config time. This is
> > consistent with how transparent hugepages can be configured.
> > 
> > Same results can be achieved with the existing
> > 'transparent_hugepage_shmem' and 'transparent_hugepage_tmpfs' settings
> > in the kernel command line, but it is more convenient to define basic
> > settings at config time instead of changing kernel command line later.
> 
> Why do you need these options instead of using CONFIG_CMDLINE?
> They should pull off exactly what you want, but without changing the kernel?

Thanks for the suggestion, Pedro. I think CONFIG_CMDLINE could work, but
for this purpose it doesn't seem ideal. Relying on CONFIG_CMDLINE isn't
a very scalable solution, since over time it tends to accumulate into a
long, unstructured string that isn't validated at build time. It also
mixes configuration layers: build-time policy and boot-time setup, which
makes the resulting behavior a bit harder to maintain in the long run.
So this approach is mainly about improving long-term maintainability and
operational clarity. I hope that makes sense.

> 
> -- 
> Pedro