From: "David Hildenbrand (Red Hat)" <david@kernel.org>
To: Kalesh Singh <kaleshsingh@google.com>,
akpm@linux-foundation.org, minchan@kernel.org,
lorenzo.stoakes@oracle.com, david@redhat.com,
Liam.Howlett@oracle.com, rppt@kernel.org, pfalcato@suse.de
Cc: rostedt@goodmis.org, hughd@google.com, kernel-team@android.com,
android-mm@google.com, Alexander Viro <viro@zeniv.linux.org.uk>,
Christian Brauner <brauner@kernel.org>, Jan Kara <jack@suse.cz>,
Kees Cook <kees@kernel.org>, Vlastimil Babka <vbabka@suse.cz>,
Suren Baghdasaryan <surenb@google.com>,
Michal Hocko <mhocko@suse.com>, Jann Horn <jannh@google.com>,
Masami Hiramatsu <mhiramat@kernel.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Valentin Schneider <vschneid@redhat.com>,
Shuah Khan <shuah@kernel.org>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org,
linux-kselftest@vger.kernel.org
Subject: Re: [PATCH v4 1/5] mm: Document lenient map_count checks
Date: Mon, 3 Nov 2025 18:08:01 +0100 [thread overview]
Message-ID: <28a5b824-f415-461c-af88-cb474ed37df1@kernel.org> (raw)
In-Reply-To: <20251028212528.681081-2-kaleshsingh@google.com>
On 28.10.25 22:24, Kalesh Singh wrote:
> Add comments to the map_count limit checks in do_mmap() and
> do_brk_flags() to clarify their intended behavior.
>
> The use of a strict inequality ('>') in these checks is intentional but
> non-obvious. It allows these functions to succeed when the VMA count is
> exactly at the sysctl_max_map_count limit. This historical behavior
> accounts for cases where the operation might not create a new VMA, but
> instead merge with or expand an existing one, in which case the VMA
> count does not increase.
>
> These comments clarify the long-standing behavior and will help prevent
> future misinterpretation as an off-by-one error.
>
> Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
> ---
Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>
--
Cheers
David
next prev parent reply other threads:[~2025-11-03 17:08 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-28 21:24 [PATCH v4 0/5] mm: Refactor and improve VMA count limit code Kalesh Singh
2025-10-28 21:24 ` [PATCH v4 1/5] mm: Document lenient map_count checks Kalesh Singh
2025-11-03 17:08 ` David Hildenbrand (Red Hat) [this message]
2025-10-28 21:24 ` [PATCH v4 2/5] mm/selftests: add max_vma_count tests Kalesh Singh
2025-11-03 17:13 ` David Hildenbrand (Red Hat)
2025-11-03 23:58 ` Kalesh Singh
2025-10-28 21:24 ` [PATCH v4 3/5] mm: Introduce max_vma_count() to abstract the max map count sysctl Kalesh Singh
2025-10-28 21:24 ` [PATCH v4 4/5] mm: rename mm_struct::map_count to vma_count Kalesh Singh
2025-10-28 21:24 ` [PATCH v4 5/5] mm/tracing: introduce trace_mm_insufficient_vma_slots event Kalesh Singh
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