Re: [PATCH v3 27/54] selftests/mm: hugepage_settings: add APIs for HugeTLB setup and teardown

[Luiz Capitulino <luizcap@redhat.com>]

On 2026-04-28 16:42, Mike Rapoport wrote:
> From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
> 
> A lot of tests require free HugeTLB pages. Some need just a few default
> huge pages, some need a certain amount of memory available as HugeTLB, and
> some just skip lots of tests if huge pages of all supported sizes are not
> available.
> 
> This all resulted in a huge mess in run_vmtests.sh that sets up some huge
> pages, adjusts them later and restores some of the settings if the stars
> align.
> 
> Add APIs that allow saving the state of HugeTLB and setting up the desired
> amount of HugeTLB pages.
> 
> Saving the state also registers atexit() callback and signal handler that
> will ensure restoration of HugeTLB state.
> 
> Since many tests use both HugeTLB and THP, the atexit() callbacks and
> signal handler are restoring both.
> 
> For kselftest_harness tests that run fixture setups and test in child
> processes add a constructor that will save and restore settings in the main
> process.
> 
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> ---
>   .../testing/selftests/mm/hugepage_settings.c  | 178 +++++++++++++++---
>   .../testing/selftests/mm/hugepage_settings.h  |  30 ++-
>   2 files changed, 183 insertions(+), 25 deletions(-)
> 
> diff --git a/tools/testing/selftests/mm/hugepage_settings.c b/tools/testing/selftests/mm/hugepage_settings.c
> index 4ae7332b5e1b..9d31b53dbc67 100644
> --- a/tools/testing/selftests/mm/hugepage_settings.c
> +++ b/tools/testing/selftests/mm/hugepage_settings.c
> @@ -306,31 +306,12 @@ void thp_restore_settings(void)
>   		thp_write_settings(&saved_settings);
>   }
>   
> -static void thp_restore_settings_atexit(void)
> +static void __thp_save_settings(void)
>   {
> -	thp_restore_settings();
> -}
> -
> -static void thp_restore_settings_sighandler(int sig)
> -{
> -	/* exit() will invoke the thp_restore_settings_atexit handler. */
> -	exit(KSFT_FAIL);
> -}
> +	if (!thp_available())
> +		return;
>   
> -void thp_save_settings(void)
> -{
>   	thp_read_settings(&saved_settings);
> -
> -	/*
> -	 * setup exit hooks to make sure THP settings are restored on graceful
> -	 * and error exits and signals
> -	 */
> -	atexit(thp_restore_settings_atexit);
> -	signal(SIGTERM, thp_restore_settings_sighandler);
> -	signal(SIGINT, thp_restore_settings_sighandler);
> -	signal(SIGHUP, thp_restore_settings_sighandler);
> -	signal(SIGQUIT, thp_restore_settings_sighandler);
> -
>   	thp_settings_saved = true;
>   }
>   
> @@ -399,11 +380,31 @@ bool thp_is_enabled(void)
>   	return mode == 1 || mode == 3;
>   }
>   
> +#define HUGETLB_MAX_NR_PAGESIZES 10
> +struct hugetlb_settings {
> +	unsigned long free_hugepages[HUGETLB_MAX_NR_PAGESIZES];

It looks like we don't actually use this in the API or maybe I'm missing
something?

Otherwise, the API looks great to me. But if you allow me to bikeshed :)

I think I'd do:

struct hugetlb_state {
	unsigned long nr_hugepages;
	unsigned long size;
};

struct hugetlb_settings {
	struct hugetlb_state hstate[HUGETLB_MAX_PAGESIZES];
	unsigned long default_size;
	int nr_sizes;
};

Maybe for the future...

> +	unsigned long nr_hugepages[HUGETLB_MAX_NR_PAGESIZES];
> +	unsigned long sizes[HUGETLB_MAX_NR_PAGESIZES];
> +	unsigned long default_size;
> +	int nr_sizes;
> +};
> +
> +static struct hugetlb_settings hugetlb_saved_settings;
> +bool hugetlb_settings_saved;
> +
>   int detect_hugetlb_page_sizes(unsigned long sizes[], int max)
>   {
> -	DIR *dir = opendir("/sys/kernel/mm/hugepages/");
> +	static struct hugetlb_settings *settings = &hugetlb_saved_settings;
> +	DIR *dir;
>   	int count = 0;
>   
> +	if (settings->nr_sizes) {
> +		for (count = 0; count < settings->nr_sizes; count++)
> +			sizes[count] = settings->sizes[count];
> +		return settings->nr_sizes;
> +	}
> +
> +	dir = opendir("/sys/kernel/mm/hugepages/");
>   	if (!dir)
>   		return 0;
>   
> @@ -427,11 +428,16 @@ int detect_hugetlb_page_sizes(unsigned long sizes[], int max)
>   
>   unsigned long default_huge_page_size(void)
>   {
> +	static struct hugetlb_settings *settings = &hugetlb_saved_settings;
>   	unsigned long hps = 0;
>   	char *line = NULL;
>   	size_t linelen = 0;
> -	FILE *f = fopen("/proc/meminfo", "r");
> +	FILE *f;
>   
> +	if (settings->default_size)
> +		return settings->default_size;
> +
> +	f = fopen("/proc/meminfo", "r");
>   	if (!f)
>   		return 0;
>   	while (getline(&line, &linelen, f) > 0) {
> @@ -479,3 +485,127 @@ unsigned long hugetlb_free_pages(unsigned long size)
>   
>   	return read_num(path);
>   }
> +
> +bool hugetlb_setup_default(unsigned long nr)
> +{
> +	unsigned long size;
> +
> +	hugetlb_save_settings();
> +
> +	size = default_huge_page_size();
> +	hugetlb_set_nr_pages(size, nr);
> +
> +	return hugetlb_free_pages(size) == nr;
> +}
> +
> +unsigned long hugetlb_setup(unsigned long nr, unsigned long sizes[],
> +			    int max)
> +{
> +	unsigned long enabled[10];
> +	int nr_sizes = 0;
> +	int nr_enabled;
> +
> +	hugetlb_save_settings();
> +
> +	nr_enabled = detect_hugetlb_page_sizes(enabled, ARRAY_SIZE(enabled));
> +	if (!nr_enabled)
> +		return 0;
> +
> +	if (nr_enabled > max) {
> +		ksft_print_msg("detected %d huge page sizes, will only test %d\n", nr_enabled, max);
> +		nr_enabled = max;
> +	}
> +
> +	/* If HugeTLB is supported, request 2 HugeTLB pages of every size. */
> +	for (int i = 0; i < nr_enabled; i++) {
> +		hugetlb_set_nr_pages(enabled[i], nr);
> +		if (hugetlb_free_pages(enabled[i]) < nr)
> +			continue;
> +
> +		sizes[nr_sizes++] = enabled[i];
> +	}
> +
> +	return nr_sizes;
> +}
> +
> +static void __hugetlb_save_settings(void)
> +{
> +	struct hugetlb_settings *settings = &hugetlb_saved_settings;
> +	int nr_sizes;
> +
> +	settings->default_size = default_huge_page_size();
> +	if (!settings->default_size)
> +		return;
> +
> +	nr_sizes = detect_hugetlb_page_sizes(settings->sizes,
> +					     HUGETLB_MAX_NR_PAGESIZES);
> +	if (!nr_sizes) {
> +		settings->default_size = 0;
> +		return;
> +	}
> +
> +	for (int i = 0; i < nr_sizes; i++) {
> +		unsigned long sz = settings->sizes[i];
> +
> +		if (!sz)
> +			continue;
> +
> +		settings->free_hugepages[i] = hugetlb_free_pages(sz);
> +		settings->nr_hugepages[i] = hugetlb_nr_pages(sz);
> +	}
> +
> +	settings->nr_sizes = nr_sizes;
> +	hugetlb_settings_saved = true;
> +}
> +
> +void hugetlb_restore_settings(void)
> +{
> +	struct hugetlb_settings *settings = &hugetlb_saved_settings;
> +
> +	if (!hugetlb_settings_saved || !settings->default_size)
> +		return;
> +
> +	for (int i = 0; i < HUGETLB_MAX_NR_PAGESIZES; i++) {
> +		unsigned long sz = settings->sizes[i];
> +
> +		if (!sz)
> +			continue;
> +
> +		hugetlb_set_nr_pages(sz, settings->nr_hugepages[i]);
> +	}
> +}
> +
> +static void hugepage_restore_settings_atexit(void)
> +{
> +	if (thp_settings_saved)
> +		thp_restore_settings();
> +	if (hugetlb_settings_saved)
> +		hugetlb_restore_settings();
> +}
> +
> +static void hugepage_restore_settings_sighandler(int sig)
> +{
> +	/* exit() will invoke the hugetlb_restore_settings_atexit handler. */
> +	exit(KSFT_FAIL);
> +}
> +
> +void hugepage_save_settings(bool thp, bool hugetlb)
> +{
> +	if (!thp && !hugetlb)
> +		return;
> +
> +	if (thp)
> +		__thp_save_settings();
> +	if (hugetlb)
> +		__hugetlb_save_settings();
> +
> +	/*
> +	 * setup exit hooks to make sure THP settings are restored on graceful
> +	 * and error exits and signals
> +	 */
> +	atexit(hugepage_restore_settings_atexit);
> +	signal(SIGTERM, hugepage_restore_settings_sighandler);
> +	signal(SIGINT, hugepage_restore_settings_sighandler);
> +	signal(SIGHUP, hugepage_restore_settings_sighandler);
> +	signal(SIGQUIT, hugepage_restore_settings_sighandler);
> +}
> diff --git a/tools/testing/selftests/mm/hugepage_settings.h b/tools/testing/selftests/mm/hugepage_settings.h
> index 57fbf2f57e13..d6a1b4e5f734 100644
> --- a/tools/testing/selftests/mm/hugepage_settings.h
> +++ b/tools/testing/selftests/mm/hugepage_settings.h
> @@ -6,6 +6,8 @@
>   #include <stddef.h>
>   #include <stdint.h>
>   
> +void hugepage_save_settings(bool thp, bool hugetlb);
> +
>   /* Transparent Huge Pages (THP) */
>   
>   enum thp_enabled {
> @@ -79,7 +81,11 @@ struct thp_settings *thp_current_settings(void);
>   void thp_push_settings(struct thp_settings *settings);
>   void thp_pop_settings(void);
>   void thp_restore_settings(void);
> -void thp_save_settings(void);
> +
> +static inline void thp_save_settings(void)
> +{
> +	hugepage_save_settings(/* thp = */ true, /* hugetlb = */ false);
> +}
>   
>   void thp_set_read_ahead_path(char *path);
>   unsigned long thp_supported_orders(void);
> @@ -97,6 +103,13 @@ unsigned long hugetlb_nr_pages(unsigned long size);
>   void hugetlb_set_nr_pages(unsigned long size, unsigned long nr);
>   unsigned long hugetlb_free_pages(unsigned long size);
>   
> +static inline void hugetlb_save_settings(void)
> +{
> +	hugepage_save_settings(/* thp = */ false, /* hugetlb = */ true);
> +}
> +
> +void hugetlb_restore_settings(void);
> +
>   static inline unsigned long hugetlb_nr_default_pages(void)
>   {
>   	unsigned long size = default_huge_page_size();
> @@ -127,4 +140,19 @@ static inline unsigned long hugetlb_free_default_pages(void)
>   	return hugetlb_free_pages(size);
>   }
>   
> +static inline bool hugetlb_available(void)
> +{
> +	return default_huge_page_size() != 0;
> +}
> +
> +bool hugetlb_setup_default(unsigned long nr);
> +unsigned long hugetlb_setup(unsigned long nr, unsigned long sizes[],
> +			    int max);
> +
> +#define HUGETLB_SETUP_DEFAULT_PAGES(nr_pages) \
> +static void __attribute__((constructor)) __hugetlb_setup_default(void)	\
> +{									\
> +	hugetlb_setup_default((nr_pages));				\
> +}
> +
>   #endif /* __THP_SETTINGS_H__ */