+ cpumask-create-dedicated-kmem-cache-for-cpumask-var.patch added to mm-nonmm-unstable branch

+ cpumask-create-dedicated-kmem-cache-for-cpumask-var.patch added to mm-nonmm-unstable branch

[Andrew Morton]

The patch titled
     Subject: cpumask: create dedicated kmem cache for cpumask var
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     cpumask-create-dedicated-kmem-cache-for-cpumask-var.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/cpumask-create-dedicated-kmem-cache-for-cpumask-var.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Dawei Li <dawei.li@shingroup.cn>
Subject: cpumask: create dedicated kmem cache for cpumask var
Date: Tue, 19 Mar 2024 20:24:00 +0800

alloc_cpumask_var_node() and friends allocate cpumask var dynamically
for CONFIG_CPUMASK_OFFSTACK=y kernel. The allocated size of cpumask var
is cpumask_size(), which is runtime constant after nr_cpu_ids is
freezed.

Create a dedicated kmem cache for dynamic allocation of cpumask var.

The window for creation of cache is somewhat narrow:
- After last update of nr_cpu_ids(via set_nr_cpu_ids())
- After kmem cache is available.
- Before any alloc_cpumask_var_node() invocations(sched_init() e.g).

Link: https://lkml.kernel.org/r/20240319122400.399516-1-dawei.li@shingroup.cn
Signed-off-by: Dawei Li <dawei.li@shingroup.cn>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Yury Norov <yury.norov@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/cpumask.h |    7 +++++++
 init/main.c             |    1 +
 lib/cpumask.c           |   15 +++++++++++++--
 3 files changed, 21 insertions(+), 2 deletions(-)

--- a/include/linux/cpumask.h~cpumask-create-dedicated-kmem-cache-for-cpumask-var
+++ a/include/linux/cpumask.h
@@ -902,6 +902,8 @@ typedef struct cpumask *cpumask_var_t;
 #define this_cpu_cpumask_var_ptr(x)	this_cpu_read(x)
 #define __cpumask_var_read_mostly	__read_mostly
 
+int __init cpumask_cache_init(void);
+
 bool alloc_cpumask_var_node(cpumask_var_t *mask, gfp_t flags, int node);
 
 static inline
@@ -949,6 +951,11 @@ typedef struct cpumask cpumask_var_t[1];
 #define this_cpu_cpumask_var_ptr(x) this_cpu_ptr(x)
 #define __cpumask_var_read_mostly
 
+static inline int cpumask_cache_init(void)
+{
+	return 0;
+}
+
 static inline bool alloc_cpumask_var(cpumask_var_t *mask, gfp_t flags)
 {
 	return true;
--- a/init/main.c~cpumask-create-dedicated-kmem-cache-for-cpumask-var
+++ a/init/main.c
@@ -931,6 +931,7 @@ void start_kernel(void)
 	sort_main_extable();
 	trap_init();
 	mm_core_init();
+	cpumask_cache_init();
 	poking_init();
 	ftrace_init();
 
--- a/lib/cpumask.c~cpumask-create-dedicated-kmem-cache-for-cpumask-var
+++ a/lib/cpumask.c
@@ -57,9 +57,20 @@ EXPORT_SYMBOL(cpumask_next_wrap);
  * CONFIG_CPUMASK_OFFSTACK=n, so does code elimination in that case
  * too.
  */
+
+static struct kmem_cache *cpumask_cache __ro_after_init;
+
+int __init cpumask_cache_init(void)
+{
+	cpumask_cache = kmem_cache_create("cpumask", cpumask_size(), sizeof(long),
+					  SLAB_HWCACHE_ALIGN, NULL);
+
+	return cpumask_cache ? 0 : -ENOMEM;
+}
+
 bool alloc_cpumask_var_node(cpumask_var_t *mask, gfp_t flags, int node)
 {
-	*mask = kmalloc_node(cpumask_size(), flags, node);
+	*mask = kmem_cache_alloc_node(cpumask_cache, flags, node);
 
 #ifdef CONFIG_DEBUG_PER_CPU_MAPS
 	if (!*mask) {
@@ -97,7 +108,7 @@ void __init alloc_bootmem_cpumask_var(cp
  */
 void free_cpumask_var(cpumask_var_t mask)
 {
-	kfree(mask);
+	kmem_cache_free(cpumask_cache, mask);
 }
 EXPORT_SYMBOL(free_cpumask_var);
 
_

Patches currently in -mm which might be from dawei.li@shingroup.cn are

cpumask-create-dedicated-kmem-cache-for-cpumask-var.patch