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

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Message-ID: <1308de0e-bb5a-481f-a447-ee4440ffb419@redhat.com>
Date: Wed, 17 Sep 2025 12:58:35 +0200
From: David Hildenbrand <david@...hat.com>
To: Kalesh Singh <kaleshsingh@...gle.com>, akpm@...ux-foundation.org,
 minchan@...nel.org, lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com,
 rppt@...nel.org, pfalcato@...e.de
Cc: 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

> + * 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
> + *
>

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?

-- 
Cheers

David / dhildenb