Re: [patch 1/3] lib: test_vmstat: add synthetic benchmark for vm stats

[Usama Arif <usama.arif@linux.dev>]

On Thu, 30 Jul 2026 21:26:23 -0700 (PDT) David Rientjes <rientjes@google.com> wrote:

> From: Christoph Lameter <cl@gentwo.org>
> 
> Add a synthetic benchmark that can be used to measure performance of VM
> statistics.  This is used to analyze any improvements or regressions in
> functions that are frequently used in hot code paths.
> 
> The test is run by inserting the module: modprobe test_vmstat
> The module insertion will always fail so that it is automatically
> unloaded; the results are in the kernel log.
> 
> Signed-off-by: Christoph Lameter <cl@gentwo.org>
> Signed-off-by: David Rientjes <rientjes@google.com>
> ---
>  lib/Kconfig.debug | 10 +++++
>  lib/Makefile      |  1 +
>  lib/test_vmstat.c | 95 +++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 106 insertions(+)
>  create mode 100644 lib/test_vmstat.c
> 
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 1244dcac2294..6d743c8e27fa 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -3427,6 +3427,16 @@ config TEST_KEXEC_HANDOVER
>  
>  	  If unsure, say N.
>  
> +config TEST_VMSTAT
> +	tristate "VM Statistics Benchmark"
> +	default n
> +	help
> +	  A synthetic benchmark measuring the performance of VM statistics,
> +	  useful to analyze any improvements or regressions in functions that
> +	  are frequently used in hot code paths.
> +
> +	  If unsure, say N.
> +
>  config RATELIMIT_KUNIT_TEST
>  	tristate "KUnit Test for correctness and stress of ratelimit" if !KUNIT_ALL_TESTS
>  	depends on KUNIT
> diff --git a/lib/Makefile b/lib/Makefile
> index 7f75cc6edf94..5f3ebabd0224 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -105,6 +105,7 @@ obj-$(CONFIG_TEST_FREE_PAGES) += test_free_pages.o
>  obj-$(CONFIG_TEST_REF_TRACKER) += test_ref_tracker.o
>  obj-$(CONFIG_TEST_OBJPOOL) += test_objpool.o
>  obj-$(CONFIG_TEST_KEXEC_HANDOVER) += test_kho.o
> +obj-$(CONFIG_TEST_VMSTAT) += test_vmstat.o
>  
>  obj-$(CONFIG_TEST_FPU) += test_fpu.o
>  test_fpu-y := test_fpu_glue.o test_fpu_impl.o
> diff --git a/lib/test_vmstat.c b/lib/test_vmstat.c
> new file mode 100644
> index 000000000000..f63f439ab9d2
> --- /dev/null
> +++ b/lib/test_vmstat.c
> @@ -0,0 +1,95 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Test module for in-kernel synthetic vm statistics performance.
> + *
> + * execute
> + *
> + *	modprobe test_vmstat
> + *
> + * to run this test
> + *
> + * (C) 2009 Linux Foundation, Christoph Lameter <cl@gentwo.org>
> + */
> +
> +#include <linux/jiffies.h>
> +#include <linux/compiler.h>
> +#include <linux/init.h>
> +#include <linux/module.h>
> +#include <linux/mm.h>
> +#include <asm/timex.h>
> +
> +#define TEST_COUNT 10000
> +
> +static int vmstat_test_init(void)
> +{
> +	unsigned int i;
> +	cycles_t time1, time2, time;
> +	int rem;
> +	struct page *page = alloc_page(GFP_KERNEL);
> +

Good to check page != NULL before using it below.

> +	pr_alert("VMstat testing\n");
> +	pr_alert("=====================\n");
> +	pr_alert("1. inc_zone_page_state() then dec_zone_page_state()\n");
> +	time1 = get_cycles();
> +	for (i = 0; i < TEST_COUNT; i++)
> +		inc_zone_page_state(page, NR_FREE_CMA_PAGES);
> +
> +	time2 = get_cycles();
> +	time = time2 - time1;
> +
> +	pr_alert("%i times inc_zone_page_state() ", i);
> +	time = div_u64_rem(time, TEST_COUNT, &rem);
> +	pr_cont("-> %llu cycles ", (unsigned long long) time);
> +
> +	time1 = get_cycles();
> +	for (i = 0; i < TEST_COUNT; i++)
> +		__dec_zone_page_state(page, NR_FREE_CMA_PAGES);

Why use inc_zone_page_state() but the __ variant for decrement?

Checking the 2 functions, __dec_zone_page_state() might cause
problems if preemption is enabled?

> +
> +	time2 = get_cycles();
> +	time = time2 - time1;
> +
> +	pr_cont("__dec_z_p_s() ");
> +	time = div_u64_rem(time, TEST_COUNT, &rem);
> +	pr_cont("-> %llu cycles\n",  (unsigned long long) time);
> +
> +	pr_alert("2. inc_zone_page_state()/dec_zone_page_state()\n");
> +	time1 = get_cycles();
> +	for (i = 0; i < TEST_COUNT; i++) {
> +		inc_zone_page_state(page, NR_FREE_CMA_PAGES);
> +		dec_zone_page_state(page, NR_FREE_CMA_PAGES);
> +	}
> +
> +	time2 = get_cycles();
> +	time = time2 - time1;
> +
> +	pr_alert("%i times inc/dec ", i);
> +	time = div_u64_rem(time, TEST_COUNT, &rem);
> +	pr_cont("-> %llu cycles\n",  (unsigned long long) time);
> +
> +	pr_alert("3. count_vm_event()\n");
> +	time1 = get_cycles();
> +	for (i = 0; i < TEST_COUNT; i++)
> +		count_vm_event(SLABS_SCANNED);
> +
> +	time2 = get_cycles();
> +	time = time2 - time1;
> +
> +	count_vm_events(SLABS_SCANNED, -TEST_COUNT);
> +	pr_alert("%i count_vm_events ", i);
> +	time = div_u64_rem(time, TEST_COUNT, &rem);
> +	pr_cont("-> %llu cycles\n",  (unsigned long long) time);
> +	__free_page(page);
> +	return -EAGAIN; /* Fail will directly unload the module */
> +}
> +
> +static void vmstat_test_exit(void)
> +{
> +	pr_alert("test exit\n");
> +}
> +
> +module_init(vmstat_test_init)
> +module_exit(vmstat_test_exit)
> +
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("Christoph Lameter");
> +MODULE_DESCRIPTION("VM statistics test");
> 
>