linux-kernel - [PATCH 1/2] mm: Mark nr_node_ids __ro_after

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Date:   Wed, 02 Aug 2023 13:24:59 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     yury.norov@...il.com, andriy.shevchenko@...ux.intel.com,
        linux@...musvillemoes.dk
Cc:     peterz@...radead.org, Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        tglx@...utronix.de, rppt@...nel.org
Subject: [PATCH 1/2] mm: Mark nr_node_ids __ro_after_init

Just like nr_cpu_ids, nr_node_ids covers the side of possible_map and
is thus constant after init.

Mark the variable __ro_after_init to both improve performance and
enhance security, since the variable is exported. A module writing to
it would be 'unfortunate'.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 mm/page_alloc.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -305,7 +305,7 @@ int movable_zone;
 EXPORT_SYMBOL(movable_zone);
 
 #if MAX_NUMNODES > 1
-unsigned int nr_node_ids __read_mostly = MAX_NUMNODES;
+unsigned int nr_node_ids __ro_after_init = MAX_NUMNODES;
 unsigned int nr_online_nodes __read_mostly = 1;
 EXPORT_SYMBOL(nr_node_ids);
 EXPORT_SYMBOL(nr_online_nodes);