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From:   Alistair Popple <apopple@nvidia.com>
To:     Ryan Roberts <ryan.roberts@arm.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Matthew Wilcox <willy@infradead.org>,
        Yin Fengwei <fengwei.yin@intel.com>,
        David Hildenbrand <david@redhat.com>,
        Yu Zhao <yuzhao@google.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Anshuman Khandual <anshuman.khandual@arm.com>,
        Yang Shi <shy828301@gmail.com>,
        "Huang, Ying" <ying.huang@intel.com>, Zi Yan <ziy@nvidia.com>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Itaru Kitayama <itaru.kitayama@gmail.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        John Hubbard <jhubbard@nvidia.com>,
        David Rientjes <rientjes@google.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Hugh Dickins <hughd@google.com>,
        Kefeng Wang <wangkefeng.wang@huawei.com>, linux-mm@kvack.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [RESEND PATCH v7 06/10] selftests/mm: Factor out thp settings
 management
Date:   Thu, 23 Nov 2023 17:07:28 +1100
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Ryan Roberts <ryan.roberts@arm.com> writes:

> The khugepaged test has a useful framework for save/restore/pop/push of
> all thp settings via the sysfs interface. This will be useful to
> explicitly control small-sized THP settings in other tests, so let's
> move it out of khugepaged and into its own thp_settings.[c|h] utility.
>
> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>

I've only glanced at the code as I assume it is a straight forward
cut-and-paste with no behavioural change. At least I didn't observe any
change running the khugepage test on my x86_64 development machine so
feel free to add:

Tested-by: Alistair Popple <apopple@nvidia.com>

> ---
>  tools/testing/selftests/mm/Makefile       |   4 +-
>  tools/testing/selftests/mm/khugepaged.c   | 346 ++--------------------
>  tools/testing/selftests/mm/thp_settings.c | 296 ++++++++++++++++++
>  tools/testing/selftests/mm/thp_settings.h |  71 +++++
>  4 files changed, 391 insertions(+), 326 deletions(-)
>  create mode 100644 tools/testing/selftests/mm/thp_settings.c
>  create mode 100644 tools/testing/selftests/mm/thp_settings.h
>
> diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
> index 78dfec8bc676..a3eb20c186e7 100644
> --- a/tools/testing/selftests/mm/Makefile
> +++ b/tools/testing/selftests/mm/Makefile
> @@ -117,8 +117,8 @@ TEST_FILES += va_high_addr_switch.sh
>
>  include ../lib.mk
>
> -$(TEST_GEN_PROGS): vm_util.c
> -$(TEST_GEN_FILES): vm_util.c
> +$(TEST_GEN_PROGS): vm_util.c thp_settings.c
> +$(TEST_GEN_FILES): vm_util.c thp_settings.c
>
>  $(OUTPUT)/uffd-stress: uffd-common.c
>  $(OUTPUT)/uffd-unit-tests: uffd-common.c
> diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
> index fc47a1c4944c..b15e7fd70176 100644
> --- a/tools/testing/selftests/mm/khugepaged.c
> +++ b/tools/testing/selftests/mm/khugepaged.c
> @@ -22,13 +22,13 @@
>  #include "linux/magic.h"
>
>  #include "vm_util.h"
> +#include "thp_settings.h"
>
>  #define BASE_ADDR ((void *)(1UL << 30))
>  static unsigned long hpage_pmd_size;
>  static unsigned long page_size;
>  static int hpage_pmd_nr;
>
> -#define THP_SYSFS "/sys/kernel/mm/transparent_hugepage/"
>  #define PID_SMAPS "/proc/self/smaps"
>  #define TEST_FILE "collapse_test_file"
>
> @@ -71,78 +71,7 @@ struct file_info {
>  };
>
>  static struct file_info finfo;
> -
> -enum thp_enabled {
> -	THP_ALWAYS,
> -	THP_MADVISE,
> -	THP_NEVER,
> -};
> -
> -static const char *thp_enabled_strings[] = {
> -	"always",
> -	"madvise",
> -	"never",
> -	NULL
> -};
> -
> -enum thp_defrag {
> -	THP_DEFRAG_ALWAYS,
> -	THP_DEFRAG_DEFER,
> -	THP_DEFRAG_DEFER_MADVISE,
> -	THP_DEFRAG_MADVISE,
> -	THP_DEFRAG_NEVER,
> -};
> -
> -static const char *thp_defrag_strings[] = {
> -	"always",
> -	"defer",
> -	"defer+madvise",
> -	"madvise",
> -	"never",
> -	NULL
> -};
> -
> -enum shmem_enabled {
> -	SHMEM_ALWAYS,
> -	SHMEM_WITHIN_SIZE,
> -	SHMEM_ADVISE,
> -	SHMEM_NEVER,
> -	SHMEM_DENY,
> -	SHMEM_FORCE,
> -};
> -
> -static const char *shmem_enabled_strings[] = {
> -	"always",
> -	"within_size",
> -	"advise",
> -	"never",
> -	"deny",
> -	"force",
> -	NULL
> -};
> -
> -struct khugepaged_settings {
> -	bool defrag;
> -	unsigned int alloc_sleep_millisecs;
> -	unsigned int scan_sleep_millisecs;
> -	unsigned int max_ptes_none;
> -	unsigned int max_ptes_swap;
> -	unsigned int max_ptes_shared;
> -	unsigned long pages_to_scan;
> -};
> -
> -struct settings {
> -	enum thp_enabled thp_enabled;
> -	enum thp_defrag thp_defrag;
> -	enum shmem_enabled shmem_enabled;
> -	bool use_zero_page;
> -	struct khugepaged_settings khugepaged;
> -	unsigned long read_ahead_kb;
> -};
> -
> -static struct settings saved_settings;
>  static bool skip_settings_restore;
> -
>  static int exit_status;
>
>  static void success(const char *msg)
> @@ -161,226 +90,13 @@ static void skip(const char *msg)
>  	printf(" \e[33m%s\e[0m\n", msg);
>  }
>
> -static int read_file(const char *path, char *buf, size_t buflen)
> -{
> -	int fd;
> -	ssize_t numread;
> -
> -	fd = open(path, O_RDONLY);
> -	if (fd == -1)
> -		return 0;
> -
> -	numread = read(fd, buf, buflen - 1);
> -	if (numread < 1) {
> -		close(fd);
> -		return 0;
> -	}
> -
> -	buf[numread] = '\0';
> -	close(fd);
> -
> -	return (unsigned int) numread;
> -}
> -
> -static int write_file(const char *path, const char *buf, size_t buflen)
> -{
> -	int fd;
> -	ssize_t numwritten;
> -
> -	fd = open(path, O_WRONLY);
> -	if (fd == -1) {
> -		printf("open(%s)\n", path);
> -		exit(EXIT_FAILURE);
> -		return 0;
> -	}
> -
> -	numwritten = write(fd, buf, buflen - 1);
> -	close(fd);
> -	if (numwritten < 1) {
> -		printf("write(%s)\n", buf);
> -		exit(EXIT_FAILURE);
> -		return 0;
> -	}
> -
> -	return (unsigned int) numwritten;
> -}
> -
> -static int read_string(const char *name, const char *strings[])
> -{
> -	char path[PATH_MAX];
> -	char buf[256];
> -	char *c;
> -	int ret;
> -
> -	ret = snprintf(path, PATH_MAX, THP_SYSFS "%s", name);
> -	if (ret >= PATH_MAX) {
> -		printf("%s: Pathname is too long\n", __func__);
> -		exit(EXIT_FAILURE);
> -	}
> -
> -	if (!read_file(path, buf, sizeof(buf))) {
> -		perror(path);
> -		exit(EXIT_FAILURE);
> -	}
> -
> -	c = strchr(buf, '[');
> -	if (!c) {
> -		printf("%s: Parse failure\n", __func__);
> -		exit(EXIT_FAILURE);
> -	}
> -
> -	c++;
> -	memmove(buf, c, sizeof(buf) - (c - buf));
> -
> -	c = strchr(buf, ']');
> -	if (!c) {
> -		printf("%s: Parse failure\n", __func__);
> -		exit(EXIT_FAILURE);
> -	}
> -	*c = '\0';
> -
> -	ret = 0;
> -	while (strings[ret]) {
> -		if (!strcmp(strings[ret], buf))
> -			return ret;
> -		ret++;
> -	}
> -
> -	printf("Failed to parse %s\n", name);
> -	exit(EXIT_FAILURE);
> -}
> -
> -static void write_string(const char *name, const char *val)
> -{
> -	char path[PATH_MAX];
> -	int ret;
> -
> -	ret = snprintf(path, PATH_MAX, THP_SYSFS "%s", name);
> -	if (ret >= PATH_MAX) {
> -		printf("%s: Pathname is too long\n", __func__);
> -		exit(EXIT_FAILURE);
> -	}
> -
> -	if (!write_file(path, val, strlen(val) + 1)) {
> -		perror(path);
> -		exit(EXIT_FAILURE);
> -	}
> -}
> -
> -static const unsigned long _read_num(const char *path)
> -{
> -	char buf[21];
> -
> -	if (read_file(path, buf, sizeof(buf)) < 0) {
> -		perror("read_file(read_num)");
> -		exit(EXIT_FAILURE);
> -	}
> -
> -	return strtoul(buf, NULL, 10);
> -}
> -
> -static const unsigned long read_num(const char *name)
> -{
> -	char path[PATH_MAX];
> -	int ret;
> -
> -	ret = snprintf(path, PATH_MAX, THP_SYSFS "%s", name);
> -	if (ret >= PATH_MAX) {
> -		printf("%s: Pathname is too long\n", __func__);
> -		exit(EXIT_FAILURE);
> -	}
> -	return _read_num(path);
> -}
> -
> -static void _write_num(const char *path, unsigned long num)
> -{
> -	char buf[21];
> -
> -	sprintf(buf, "%ld", num);
> -	if (!write_file(path, buf, strlen(buf) + 1)) {
> -		perror(path);
> -		exit(EXIT_FAILURE);
> -	}
> -}
> -
> -static void write_num(const char *name, unsigned long num)
> -{
> -	char path[PATH_MAX];
> -	int ret;
> -
> -	ret = snprintf(path, PATH_MAX, THP_SYSFS "%s", name);
> -	if (ret >= PATH_MAX) {
> -		printf("%s: Pathname is too long\n", __func__);
> -		exit(EXIT_FAILURE);
> -	}
> -	_write_num(path, num);
> -}
> -
> -static void write_settings(struct settings *settings)
> -{
> -	struct khugepaged_settings *khugepaged = &settings->khugepaged;
> -
> -	write_string("enabled", thp_enabled_strings[settings->thp_enabled]);
> -	write_string("defrag", thp_defrag_strings[settings->thp_defrag]);
> -	write_string("shmem_enabled",
> -			shmem_enabled_strings[settings->shmem_enabled]);
> -	write_num("use_zero_page", settings->use_zero_page);
> -
> -	write_num("khugepaged/defrag", khugepaged->defrag);
> -	write_num("khugepaged/alloc_sleep_millisecs",
> -			khugepaged->alloc_sleep_millisecs);
> -	write_num("khugepaged/scan_sleep_millisecs",
> -			khugepaged->scan_sleep_millisecs);
> -	write_num("khugepaged/max_ptes_none", khugepaged->max_ptes_none);
> -	write_num("khugepaged/max_ptes_swap", khugepaged->max_ptes_swap);
> -	write_num("khugepaged/max_ptes_shared", khugepaged->max_ptes_shared);
> -	write_num("khugepaged/pages_to_scan", khugepaged->pages_to_scan);
> -
> -	if (file_ops && finfo.type == VMA_FILE)
> -		_write_num(finfo.dev_queue_read_ahead_path,
> -			   settings->read_ahead_kb);
> -}
> -
> -#define MAX_SETTINGS_DEPTH 4
> -static struct settings settings_stack[MAX_SETTINGS_DEPTH];
> -static int settings_index;
> -
> -static struct settings *current_settings(void)
> -{
> -	if (!settings_index) {
> -		printf("Fail: No settings set");
> -		exit(EXIT_FAILURE);
> -	}
> -	return settings_stack + settings_index - 1;
> -}
> -
> -static void push_settings(struct settings *settings)
> -{
> -	if (settings_index >= MAX_SETTINGS_DEPTH) {
> -		printf("Fail: Settings stack exceeded");
> -		exit(EXIT_FAILURE);
> -	}
> -	settings_stack[settings_index++] = *settings;
> -	write_settings(current_settings());
> -}
> -
> -static void pop_settings(void)
> -{
> -	if (settings_index <= 0) {
> -		printf("Fail: Settings stack empty");
> -		exit(EXIT_FAILURE);
> -	}
> -	--settings_index;
> -	write_settings(current_settings());
> -}
> -
>  static void restore_settings_atexit(void)
>  {
>  	if (skip_settings_restore)
>  		return;
>
>  	printf("Restore THP and khugepaged settings...");
> -	write_settings(&saved_settings);
> +	thp_restore_settings();
>  	success("OK");
>
>  	skip_settings_restore = true;
> @@ -395,27 +111,9 @@ static void restore_settings(int sig)
>  static void save_settings(void)
>  {
>  	printf("Save THP and khugepaged settings...");
> -	saved_settings = (struct settings) {
> -		.thp_enabled = read_string("enabled", thp_enabled_strings),
> -		.thp_defrag = read_string("defrag", thp_defrag_strings),
> -		.shmem_enabled =
> -			read_string("shmem_enabled", shmem_enabled_strings),
> -		.use_zero_page = read_num("use_zero_page"),
> -	};
> -	saved_settings.khugepaged = (struct khugepaged_settings) {
> -		.defrag = read_num("khugepaged/defrag"),
> -		.alloc_sleep_millisecs =
> -			read_num("khugepaged/alloc_sleep_millisecs"),
> -		.scan_sleep_millisecs =
> -			read_num("khugepaged/scan_sleep_millisecs"),
> -		.max_ptes_none = read_num("khugepaged/max_ptes_none"),
> -		.max_ptes_swap = read_num("khugepaged/max_ptes_swap"),
> -		.max_ptes_shared = read_num("khugepaged/max_ptes_shared"),
> -		.pages_to_scan = read_num("khugepaged/pages_to_scan"),
> -	};
>  	if (file_ops && finfo.type == VMA_FILE)
> -		saved_settings.read_ahead_kb =
> -				_read_num(finfo.dev_queue_read_ahead_path);
> +		thp_set_read_ahead_path(finfo.dev_queue_read_ahead_path);
> +	thp_save_settings();
>
>  	success("OK");
>
> @@ -798,7 +496,7 @@ static void __madvise_collapse(const char *msg, char *p, int nr_hpages,
>  			       struct mem_ops *ops, bool expect)
>  {
>  	int ret;
> -	struct settings settings = *current_settings();
> +	struct thp_settings settings = *thp_current_settings();
>
>  	printf("%s...", msg);
>
> @@ -808,7 +506,7 @@ static void __madvise_collapse(const char *msg, char *p, int nr_hpages,
>  	 */
>  	settings.thp_enabled = THP_NEVER;
>  	settings.shmem_enabled = SHMEM_NEVER;
> -	push_settings(&settings);
> +	thp_push_settings(&settings);
>
>  	/* Clear VM_NOHUGEPAGE */
>  	madvise(p, nr_hpages * hpage_pmd_size, MADV_HUGEPAGE);
> @@ -820,7 +518,7 @@ static void __madvise_collapse(const char *msg, char *p, int nr_hpages,
>  	else
>  		success("OK");
>
> -	pop_settings();
> +	thp_pop_settings();
>  }
>
>  static void madvise_collapse(const char *msg, char *p, int nr_hpages,
> @@ -850,13 +548,13 @@ static bool wait_for_scan(const char *msg, char *p, int nr_hpages,
>  	madvise(p, nr_hpages * hpage_pmd_size, MADV_HUGEPAGE);
>
>  	/* Wait until the second full_scan completed */
> -	full_scans = read_num("khugepaged/full_scans") + 2;
> +	full_scans = thp_read_num("khugepaged/full_scans") + 2;
>
>  	printf("%s...", msg);
>  	while (timeout--) {
>  		if (ops->check_huge(p, nr_hpages))
>  			break;
> -		if (read_num("khugepaged/full_scans") >= full_scans)
> +		if (thp_read_num("khugepaged/full_scans") >= full_scans)
>  			break;
>  		printf(".");
>  		usleep(TICK);
> @@ -911,11 +609,11 @@ static bool is_tmpfs(struct mem_ops *ops)
>
>  static void alloc_at_fault(void)
>  {
> -	struct settings settings = *current_settings();
> +	struct thp_settings settings = *thp_current_settings();
>  	char *p;
>
>  	settings.thp_enabled = THP_ALWAYS;
> -	push_settings(&settings);
> +	thp_push_settings(&settings);
>
>  	p = alloc_mapping(1);
>  	*p = 1;
> @@ -925,7 +623,7 @@ static void alloc_at_fault(void)
>  	else
>  		fail("Fail");
>
> -	pop_settings();
> +	thp_pop_settings();
>
>  	madvise(p, page_size, MADV_DONTNEED);
>  	printf("Split huge PMD on MADV_DONTNEED...");
> @@ -973,11 +671,11 @@ static void collapse_single_pte_entry(struct collapse_context *c, struct mem_ops
>  static void collapse_max_ptes_none(struct collapse_context *c, struct mem_ops *ops)
>  {
>  	int max_ptes_none = hpage_pmd_nr / 2;
> -	struct settings settings = *current_settings();
> +	struct thp_settings settings = *thp_current_settings();
>  	void *p;
>
>  	settings.khugepaged.max_ptes_none = max_ptes_none;
> -	push_settings(&settings);
> +	thp_push_settings(&settings);
>
>  	p = ops->setup_area(1);
>
> @@ -1002,7 +700,7 @@ static void collapse_max_ptes_none(struct collapse_context *c, struct mem_ops *o
>  	}
>  skip:
>  	ops->cleanup_area(p, hpage_pmd_size);
> -	pop_settings();
> +	thp_pop_settings();
>  }
>
>  static void collapse_swapin_single_pte(struct collapse_context *c, struct mem_ops *ops)
> @@ -1033,7 +731,7 @@ static void collapse_swapin_single_pte(struct collapse_context *c, struct mem_op
>
>  static void collapse_max_ptes_swap(struct collapse_context *c, struct mem_ops *ops)
>  {
> -	int max_ptes_swap = read_num("khugepaged/max_ptes_swap");
> +	int max_ptes_swap = thp_read_num("khugepaged/max_ptes_swap");
>  	void *p;
>
>  	p = ops->setup_area(1);
> @@ -1250,11 +948,11 @@ static void collapse_fork_compound(struct collapse_context *c, struct mem_ops *o
>  			fail("Fail");
>  		ops->fault(p, 0, page_size);
>
> -		write_num("khugepaged/max_ptes_shared", hpage_pmd_nr - 1);
> +		thp_write_num("khugepaged/max_ptes_shared", hpage_pmd_nr - 1);
>  		c->collapse("Collapse PTE table full of compound pages in child",
>  			    p, 1, ops, true);
> -		write_num("khugepaged/max_ptes_shared",
> -			  current_settings()->khugepaged.max_ptes_shared);
> +		thp_write_num("khugepaged/max_ptes_shared",
> +			  thp_current_settings()->khugepaged.max_ptes_shared);
>
>  		validate_memory(p, 0, hpage_pmd_size);
>  		ops->cleanup_area(p, hpage_pmd_size);
> @@ -1275,7 +973,7 @@ static void collapse_fork_compound(struct collapse_context *c, struct mem_ops *o
>
>  static void collapse_max_ptes_shared(struct collapse_context *c, struct mem_ops *ops)
>  {
> -	int max_ptes_shared = read_num("khugepaged/max_ptes_shared");
> +	int max_ptes_shared = thp_read_num("khugepaged/max_ptes_shared");
>  	int wstatus;
>  	void *p;
>
> @@ -1443,7 +1141,7 @@ static void parse_test_type(int argc, const char **argv)
>
>  int main(int argc, const char **argv)
>  {
> -	struct settings default_settings = {
> +	struct thp_settings default_settings = {
>  		.thp_enabled = THP_MADVISE,
>  		.thp_defrag = THP_DEFRAG_ALWAYS,
>  		.shmem_enabled = SHMEM_ADVISE,
> @@ -1484,7 +1182,7 @@ int main(int argc, const char **argv)
>  	default_settings.khugepaged.pages_to_scan = hpage_pmd_nr * 8;
>
>  	save_settings();
> -	push_settings(&default_settings);
> +	thp_push_settings(&default_settings);
>
>  	alloc_at_fault();
>
> diff --git a/tools/testing/selftests/mm/thp_settings.c b/tools/testing/selftests/mm/thp_settings.c
> new file mode 100644
> index 000000000000..5e8ec792cac7
> --- /dev/null
> +++ b/tools/testing/selftests/mm/thp_settings.c
> @@ -0,0 +1,296 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <fcntl.h>
> +#include <limits.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <unistd.h>
> +
> +#include "thp_settings.h"
> +
> +#define THP_SYSFS "/sys/kernel/mm/transparent_hugepage/"
> +#define MAX_SETTINGS_DEPTH 4
> +static struct thp_settings settings_stack[MAX_SETTINGS_DEPTH];
> +static int settings_index;
> +static struct thp_settings saved_settings;
> +static char dev_queue_read_ahead_path[PATH_MAX];
> +
> +static const char * const thp_enabled_strings[] = {
> +	"always",
> +	"madvise",
> +	"never",
> +	NULL
> +};
> +
> +static const char * const thp_defrag_strings[] = {
> +	"always",
> +	"defer",
> +	"defer+madvise",
> +	"madvise",
> +	"never",
> +	NULL
> +};
> +
> +static const char * const shmem_enabled_strings[] = {
> +	"always",
> +	"within_size",
> +	"advise",
> +	"never",
> +	"deny",
> +	"force",
> +	NULL
> +};
> +
> +int read_file(const char *path, char *buf, size_t buflen)
> +{
> +	int fd;
> +	ssize_t numread;
> +
> +	fd = open(path, O_RDONLY);
> +	if (fd == -1)
> +		return 0;
> +
> +	numread = read(fd, buf, buflen - 1);
> +	if (numread < 1) {
> +		close(fd);
> +		return 0;
> +	}
> +
> +	buf[numread] = '\0';
> +	close(fd);
> +
> +	return (unsigned int) numread;
> +}
> +
> +int write_file(const char *path, const char *buf, size_t buflen)
> +{
> +	int fd;
> +	ssize_t numwritten;
> +
> +	fd = open(path, O_WRONLY);
> +	if (fd == -1) {
> +		printf("open(%s)\n", path);
> +		exit(EXIT_FAILURE);
> +		return 0;
> +	}
> +
> +	numwritten = write(fd, buf, buflen - 1);
> +	close(fd);
> +	if (numwritten < 1) {
> +		printf("write(%s)\n", buf);
> +		exit(EXIT_FAILURE);
> +		return 0;
> +	}
> +
> +	return (unsigned int) numwritten;
> +}
> +
> +const unsigned long read_num(const char *path)
> +{
> +	char buf[21];
> +
> +	if (read_file(path, buf, sizeof(buf)) < 0) {
> +		perror("read_file()");
> +		exit(EXIT_FAILURE);
> +	}
> +
> +	return strtoul(buf, NULL, 10);
> +}
> +
> +void write_num(const char *path, unsigned long num)
> +{
> +	char buf[21];
> +
> +	sprintf(buf, "%ld", num);
> +	if (!write_file(path, buf, strlen(buf) + 1)) {
> +		perror(path);
> +		exit(EXIT_FAILURE);
> +	}
> +}
> +
> +int thp_read_string(const char *name, const char * const strings[])
> +{
> +	char path[PATH_MAX];
> +	char buf[256];
> +	char *c;
> +	int ret;
> +
> +	ret = snprintf(path, PATH_MAX, THP_SYSFS "%s", name);
> +	if (ret >= PATH_MAX) {
> +		printf("%s: Pathname is too long\n", __func__);
> +		exit(EXIT_FAILURE);
> +	}
> +
> +	if (!read_file(path, buf, sizeof(buf))) {
> +		perror(path);
> +		exit(EXIT_FAILURE);
> +	}
> +
> +	c = strchr(buf, '[');
> +	if (!c) {
> +		printf("%s: Parse failure\n", __func__);
> +		exit(EXIT_FAILURE);
> +	}
> +
> +	c++;
> +	memmove(buf, c, sizeof(buf) - (c - buf));
> +
> +	c = strchr(buf, ']');
> +	if (!c) {
> +		printf("%s: Parse failure\n", __func__);
> +		exit(EXIT_FAILURE);
> +	}
> +	*c = '\0';
> +
> +	ret = 0;
> +	while (strings[ret]) {
> +		if (!strcmp(strings[ret], buf))
> +			return ret;
> +		ret++;
> +	}
> +
> +	printf("Failed to parse %s\n", name);
> +	exit(EXIT_FAILURE);
> +}
> +
> +void thp_write_string(const char *name, const char *val)
> +{
> +	char path[PATH_MAX];
> +	int ret;
> +
> +	ret = snprintf(path, PATH_MAX, THP_SYSFS "%s", name);
> +	if (ret >= PATH_MAX) {
> +		printf("%s: Pathname is too long\n", __func__);
> +		exit(EXIT_FAILURE);
> +	}
> +
> +	if (!write_file(path, val, strlen(val) + 1)) {
> +		perror(path);
> +		exit(EXIT_FAILURE);
> +	}
> +}
> +
> +const unsigned long thp_read_num(const char *name)
> +{
> +	char path[PATH_MAX];
> +	int ret;
> +
> +	ret = snprintf(path, PATH_MAX, THP_SYSFS "%s", name);
> +	if (ret >= PATH_MAX) {
> +		printf("%s: Pathname is too long\n", __func__);
> +		exit(EXIT_FAILURE);
> +	}
> +	return read_num(path);
> +}
> +
> +void thp_write_num(const char *name, unsigned long num)
> +{
> +	char path[PATH_MAX];
> +	int ret;
> +
> +	ret = snprintf(path, PATH_MAX, THP_SYSFS "%s", name);
> +	if (ret >= PATH_MAX) {
> +		printf("%s: Pathname is too long\n", __func__);
> +		exit(EXIT_FAILURE);
> +	}
> +	write_num(path, num);
> +}
> +
> +void thp_read_settings(struct thp_settings *settings)
> +{
> +	*settings = (struct thp_settings) {
> +		.thp_enabled = thp_read_string("enabled", thp_enabled_strings),
> +		.thp_defrag = thp_read_string("defrag", thp_defrag_strings),
> +		.shmem_enabled =
> +			thp_read_string("shmem_enabled", shmem_enabled_strings),
> +		.use_zero_page = thp_read_num("use_zero_page"),
> +	};
> +	settings->khugepaged = (struct khugepaged_settings) {
> +		.defrag = thp_read_num("khugepaged/defrag"),
> +		.alloc_sleep_millisecs =
> +			thp_read_num("khugepaged/alloc_sleep_millisecs"),
> +		.scan_sleep_millisecs =
> +			thp_read_num("khugepaged/scan_sleep_millisecs"),
> +		.max_ptes_none = thp_read_num("khugepaged/max_ptes_none"),
> +		.max_ptes_swap = thp_read_num("khugepaged/max_ptes_swap"),
> +		.max_ptes_shared = thp_read_num("khugepaged/max_ptes_shared"),
> +		.pages_to_scan = thp_read_num("khugepaged/pages_to_scan"),
> +	};
> +	if (dev_queue_read_ahead_path[0])
> +		settings->read_ahead_kb = read_num(dev_queue_read_ahead_path);
> +}
> +
> +void thp_write_settings(struct thp_settings *settings)
> +{
> +	struct khugepaged_settings *khugepaged = &settings->khugepaged;
> +
> +	thp_write_string("enabled", thp_enabled_strings[settings->thp_enabled]);
> +	thp_write_string("defrag", thp_defrag_strings[settings->thp_defrag]);
> +	thp_write_string("shmem_enabled",
> +			shmem_enabled_strings[settings->shmem_enabled]);
> +	thp_write_num("use_zero_page", settings->use_zero_page);
> +
> +	thp_write_num("khugepaged/defrag", khugepaged->defrag);
> +	thp_write_num("khugepaged/alloc_sleep_millisecs",
> +			khugepaged->alloc_sleep_millisecs);
> +	thp_write_num("khugepaged/scan_sleep_millisecs",
> +			khugepaged->scan_sleep_millisecs);
> +	thp_write_num("khugepaged/max_ptes_none", khugepaged->max_ptes_none);
> +	thp_write_num("khugepaged/max_ptes_swap", khugepaged->max_ptes_swap);
> +	thp_write_num("khugepaged/max_ptes_shared", khugepaged->max_ptes_shared);
> +	thp_write_num("khugepaged/pages_to_scan", khugepaged->pages_to_scan);
> +
> +	if (dev_queue_read_ahead_path[0])
> +		write_num(dev_queue_read_ahead_path, settings->read_ahead_kb);
> +}
> +
> +struct thp_settings *thp_current_settings(void)
> +{
> +	if (!settings_index) {
> +		printf("Fail: No settings set");
> +		exit(EXIT_FAILURE);
> +	}
> +	return settings_stack + settings_index - 1;
> +}
> +
> +void thp_push_settings(struct thp_settings *settings)
> +{
> +	if (settings_index >= MAX_SETTINGS_DEPTH) {
> +		printf("Fail: Settings stack exceeded");
> +		exit(EXIT_FAILURE);
> +	}
> +	settings_stack[settings_index++] = *settings;
> +	thp_write_settings(thp_current_settings());
> +}
> +
> +void thp_pop_settings(void)
> +{
> +	if (settings_index <= 0) {
> +		printf("Fail: Settings stack empty");
> +		exit(EXIT_FAILURE);
> +	}
> +	--settings_index;
> +	thp_write_settings(thp_current_settings());
> +}
> +
> +void thp_restore_settings(void)
> +{
> +	thp_write_settings(&saved_settings);
> +}
> +
> +void thp_save_settings(void)
> +{
> +	thp_read_settings(&saved_settings);
> +}
> +
> +void thp_set_read_ahead_path(char *path)
> +{
> +	if (!path) {
> +		dev_queue_read_ahead_path[0] = '\0';
> +		return;
> +	}
> +
> +	strncpy(dev_queue_read_ahead_path, path,
> +		sizeof(dev_queue_read_ahead_path));
> +	dev_queue_read_ahead_path[sizeof(dev_queue_read_ahead_path) - 1] = '\0';
> +}
> diff --git a/tools/testing/selftests/mm/thp_settings.h b/tools/testing/selftests/mm/thp_settings.h
> new file mode 100644
> index 000000000000..ff3d98c30617
> --- /dev/null
> +++ b/tools/testing/selftests/mm/thp_settings.h
> @@ -0,0 +1,71 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef __THP_SETTINGS_H__
> +#define __THP_SETTINGS_H__
> +
> +#include <stdbool.h>
> +#include <stddef.h>
> +#include <stdint.h>
> +
> +enum thp_enabled {
> +	THP_ALWAYS,
> +	THP_MADVISE,
> +	THP_NEVER,
> +};
> +
> +enum thp_defrag {
> +	THP_DEFRAG_ALWAYS,
> +	THP_DEFRAG_DEFER,
> +	THP_DEFRAG_DEFER_MADVISE,
> +	THP_DEFRAG_MADVISE,
> +	THP_DEFRAG_NEVER,
> +};
> +
> +enum shmem_enabled {
> +	SHMEM_ALWAYS,
> +	SHMEM_WITHIN_SIZE,
> +	SHMEM_ADVISE,
> +	SHMEM_NEVER,
> +	SHMEM_DENY,
> +	SHMEM_FORCE,
> +};
> +
> +struct khugepaged_settings {
> +	bool defrag;
> +	unsigned int alloc_sleep_millisecs;
> +	unsigned int scan_sleep_millisecs;
> +	unsigned int max_ptes_none;
> +	unsigned int max_ptes_swap;
> +	unsigned int max_ptes_shared;
> +	unsigned long pages_to_scan;
> +};
> +
> +struct thp_settings {
> +	enum thp_enabled thp_enabled;
> +	enum thp_defrag thp_defrag;
> +	enum shmem_enabled shmem_enabled;
> +	bool use_zero_page;
> +	struct khugepaged_settings khugepaged;
> +	unsigned long read_ahead_kb;
> +};
> +
> +int read_file(const char *path, char *buf, size_t buflen);
> +int write_file(const char *path, const char *buf, size_t buflen);
> +const unsigned long read_num(const char *path);
> +void write_num(const char *path, unsigned long num);
> +
> +int thp_read_string(const char *name, const char * const strings[]);
> +void thp_write_string(const char *name, const char *val);
> +const unsigned long thp_read_num(const char *name);
> +void thp_write_num(const char *name, unsigned long num);
> +
> +void thp_write_settings(struct thp_settings *settings);
> +void thp_read_settings(struct thp_settings *settings);
> +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);
> +
> +void thp_set_read_ahead_path(char *path);
> +
> +#endif /* __THP_SETTINGS_H__ */