linux-kernel - Re: [PATCH v2 2/7] mm/selftests: add max_vma

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Message-ID: <CAC_TJveQks8qnqTUq-tyY6VV34mPz8ZmQ9XmsDRAz0-yW535MA@mail.gmail.com>
Date: Wed, 17 Sep 2025 09:49:57 -0700
From: Kalesh Singh <kaleshsingh@...gle.com>
To: David Hildenbrand <david@...hat.com>
Cc: akpm@...ux-foundation.org, minchan@...nel.org, lorenzo.stoakes@...cle.com, 
	Liam.Howlett@...cle.com, rppt@...nel.org, pfalcato@...e.de, 
	kernel-team@...roid.com, android-mm@...gle.com, 
	Alexander Viro <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, 
	Kees Cook <kees@...nel.org>, Vlastimil Babka <vbabka@...e.cz>, Suren Baghdasaryan <surenb@...gle.com>, 
	Michal Hocko <mhocko@...e.com>, Steven Rostedt <rostedt@...dmis.org>, 
	Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, 
	Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, 
	Juri Lelli <juri.lelli@...hat.com>, Vincent Guittot <vincent.guittot@...aro.org>, 
	Dietmar Eggemann <dietmar.eggemann@....com>, Ben Segall <bsegall@...gle.com>, 
	Mel Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>, Jann Horn <jannh@...gle.com>, 
	Shuah Khan <shuah@...nel.org>, linux-kernel@...r.kernel.org, 
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org, 
	linux-trace-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2 2/7] mm/selftests: add max_vma_count tests

On Wed, Sep 17, 2025 at 3:58 AM 'David Hildenbrand' via kernel-team
<kernel-team@...roid.com> wrote:
>
> > + * test_suite_setup - Set up the VMA layout for VMA count testing.
> > + *
> > + * Sets up the following VMA layout:
> > + *
> > + * +----- base_addr
> > + * |
> > + * V
> > + * +--------------+----------------------+--------------+----------------+--------------+----------------+--------------+-----+----------------+--------------+
> > + * |  Guard Page  |                      |  Guard Page  |  Extra Map 1   | Unmapped Gap |  Extra Map 2   | Unmapped Gap | ... |  Extra Map N   | Unmapped Gap |
> > + * |  (unmapped)  |      TEST_AREA       |  (unmapped)  | (mapped page)  |  (1 page)    | (mapped page)  |  (1 page)    | ... | (mapped page)  |  (1 page)    |
> > + * |   (1 page)   | (unmapped, 3 pages)  |   (1 page)   |    (1 page)    |              |    (1 page)    |              |     |    (1 page)    |              |
> > + * +--------------+----------------------+--------------+----------------+--------------+----------------+--------------+-----+----------------+--------------+
> > + * ^              ^                      ^              ^                                                                  ^
> > + * |              |                      |              |                                                                  |
> > + * +--GUARD_SIZE--+                      |              +-- EXTRA_MAPS points here             Sufficient EXTRA_MAPS to ---+
> > + *    (PAGE_SIZE) |                      |                                                         reach MAX_VMA_COUNT
> > + *                |                      |
> > + *                +--- TEST_AREA_SIZE ---+
> > + *                |   (3 * PAGE_SIZE)    |
> > + *                ^
> > + *                |
> > + *                +-- TEST_AREA starts here
> > + *
> >
>

Hi David,

Thanks for the reviews.

> Just wondering if we could find a different name than "guard page" here,
> to not confuse stuff with guard ptes
>
> Will the current "guard page" we a valid vma or just a hole?

It's a hole to prevent coincidental merging of adjacent VMAs. I can
rename it to HOLE in the next revision.

Thanks,
Kalesh

>
> --
> Cheers
>
> David / dhildenb
>
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