Re: [RFC PATCH v7 2/2] mm: Fix OOM killer inaccuracy on large many-core systems

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

On 2025-11-07 10:53, Mathieu Desnoyers wrote:
[...]
> 
> It would make sense to call an explicit percpu counter tree init
> function from start_kernel() between the call to mm_core_init() and the
> call to maple_tree_init(). This way it would be initialized right after
> mm, but given that the hierarchical counter tree is a lib that can be
> used for other purposes than mm accounting, I think it makes sense
> to call its init explicitly from start_kernel() rather than bury
> it within mm_core_init().
See the following diff. If nobody object, I'll prepare a v8 which
includes it.

diff --git a/include/linux/percpu_counter_tree.h 
b/include/linux/percpu_counter_tree.h
index 8795e782680a..40fcdd6456b6 100644
--- a/include/linux/percpu_counter_tree.h
+++ b/include/linux/percpu_counter_tree.h
@@ -41,6 +41,7 @@ int percpu_counter_tree_precise_compare(struct 
percpu_counter_tree *a, struct pe
  int percpu_counter_tree_precise_compare_value(struct 
percpu_counter_tree *counter, int v);
  void percpu_counter_tree_set(struct percpu_counter_tree *counter, int v);
  unsigned int percpu_counter_tree_inaccuracy(struct percpu_counter_tree 
*counter);
+int percpu_counter_tree_subsystem_init(void);

  /* Fast paths */

@@ -191,6 +192,12 @@ int percpu_counter_tree_approximate_sum(struct 
percpu_counter_tree *counter)
  	return percpu_counter_tree_precise_sum(counter);
  }

+static inline
+int percpu_counter_tree_subsystem_init(void)
+{
+	return 0;
+}
+
  #endif	/* CONFIG_SMP */

  static inline
diff --git a/init/main.c b/init/main.c
index 07a3116811c5..204d9f913130 100644
--- a/init/main.c
+++ b/init/main.c
@@ -104,6 +104,7 @@
  #include <linux/pidfs.h>
  #include <linux/ptdump.h>
  #include <linux/time_namespace.h>
+#include <linux/percpu_counter_tree.h>
  #include <net/net_namespace.h>

  #include <asm/io.h>
@@ -969,6 +970,7 @@ void start_kernel(void)
  	sort_main_extable();
  	trap_init();
  	mm_core_init();
+	percpu_counter_tree_subsystem_init();
  	maple_tree_init();
  	poking_init();
  	ftrace_init();
diff --git a/lib/percpu_counter_tree.c b/lib/percpu_counter_tree.c
index 9577d94251d1..05c3db0ce5b1 100644
--- a/lib/percpu_counter_tree.c
+++ b/lib/percpu_counter_tree.c
@@ -379,7 +379,7 @@ static unsigned int __init 
calculate_inaccuracy_multiplier(void)
  	return inaccuracy;
  }

-static int __init percpu_counter_startup(void)
+int __init percpu_counter_tree_subsystem_init(void)
  {

  	nr_cpus_order = get_count_order(nr_cpu_ids);
@@ -391,4 +391,3 @@ static int __init percpu_counter_startup(void)
  	inaccuracy_multiplier = calculate_inaccuracy_multiplier();
  	return 0;
  }
-module_init(percpu_counter_startup);


-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com