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

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Message-ID: <81258c9e-1436-4a4f-9343-ef574b8b0de6@efficios.com>
Date: Fri, 7 Nov 2025 11:04:01 -0500
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Shakeel Butt <shakeel.butt@...ux.dev>,
 kernel test robot <oliver.sang@...el.com>
Cc: oe-lkp@...ts.linux.dev, lkp@...el.com,
 Andrew Morton <akpm@...ux-foundation.org>,
 "Paul E. McKenney" <paulmck@...nel.org>, Steven Rostedt
 <rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>,
 Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>,
 Christoph Lameter <cl@...ux.com>, Martin Liu <liumartin@...gle.com>,
 David Rientjes <rientjes@...gle.com>, SeongJae Park <sj@...nel.org>,
 Michal Hocko <mhocko@...e.com>, Johannes Weiner <hannes@...xchg.org>,
 Sweet Tea Dorminy <sweettea@...gle.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 "Liam R . Howlett" <liam.howlett@...cle.com>, Mike Rapoport
 <rppt@...nel.org>, Suren Baghdasaryan <surenb@...gle.com>,
 Vlastimil Babka <vbabka@...e.cz>, Christian Brauner <brauner@...nel.org>,
 Wei Yang <richard.weiyang@...il.com>, David Hildenbrand <david@...hat.com>,
 Miaohe Lin <linmiaohe@...wei.com>, Al Viro <viro@...iv.linux.org.uk>,
 Yu Zhao <yuzhao@...gle.com>, Roman Gushchin <roman.gushchin@...ux.dev>,
 Mateusz Guzik <mjguzik@...il.com>, Matthew Wilcox <willy@...radead.org>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>,
 Aboorva Devarajan <aboorvad@...ux.ibm.com>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 christian.koenig@....com
Subject: Re: [RFC PATCH v7 2/2] mm: Fix OOM killer inaccuracy on large
 many-core systems

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