selftests/cgroup/test_zswap.c

// SPDX-License-Identifier: GPL-2.0
#define _GNU_SOURCE

#include <linux/limits.h>
#include <unistd.h>
#include <stdio.h>
#include <signal.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/sysinfo.h>
#include <string.h>
#include <sys/wait.h>
#include <sys/mman.h>
#include <sys/random.h>

#include "kselftest.h"
#include "cgroup_util.h"

static int page_size;

#define PATH_ZSWAP "/sys/module/zswap"
#define PATH_ZSWAP_ENABLED "/sys/module/zswap/parameters/enabled"
#define PATH_ZSWAP_SHRINKER_ENABLED "/sys/module/zswap/parameters/shrinker_enabled"
#define PATH_ZSWAP_STORED_PAGES "/sys/kernel/debug/zswap/stored_pages"

static int read_int(const char *path, size_t *value)
{
	FILE *file;
	int ret = 0;

	file = fopen(path, "r");
	if (!file)
		return -1;
	if (fscanf(file, "%ld", value) != 1)
		ret = -1;
	fclose(file);
	return ret;
}

static int set_min_free_kb(size_t value)
{
	FILE *file;
	int ret;

	file = fopen("/proc/sys/vm/min_free_kbytes", "w");
	if (!file)
		return -1;
	ret = fprintf(file, "%ld\n", value);
	fclose(file);
	return ret;
}

static int read_min_free_kb(size_t *value)
{
	return read_int("/proc/sys/vm/min_free_kbytes", value);
}

static int get_zswap_stored_pages(size_t *value)
{
	return read_int(PATH_ZSWAP_STORED_PAGES, value);
}

static long get_cg_wb_count(const char *cg)
{
	return cg_read_key_long(cg, "memory.stat", "zswpwb");
}

static long get_zswpout(const char *cgroup)
{
	return cg_read_key_long(cgroup, "memory.stat", "zswpout ");
}

static int allocate_and_read_bytes(const char *cgroup, void *arg)
{
	size_t size = (size_t)arg;
	char *mem = (char *)malloc(size);
	int ret = 0;

	if (!mem)
		return -1;
	for (int i = 0; i < size; i += page_size)
		mem[i] = 'a';

	/* Go through the allocated memory to (z)swap in and out pages */
	for (int i = 0; i < size; i += page_size) {
		if (mem[i] != 'a')
			ret = -1;
	}

	free(mem);
	return ret;
}

static int allocate_bytes(const char *cgroup, void *arg)
{
	size_t size = (size_t)arg;
	char *mem = (char *)malloc(size);

	if (!mem)
		return -1;
	for (int i = 0; i < size; i += page_size)
		mem[i] = 'a';
	free(mem);
	return 0;
}

static char *setup_test_group_1M(const char *root, const char *name)
{
	char *group_name = cg_name(root, name);

	if (!group_name)
		return NULL;
	if (cg_create(group_name))
		goto fail;
	if (cg_write(group_name, "memory.max", "1M")) {
		cg_destroy(group_name);
		goto fail;
	}
	return group_name;
fail:
	free(group_name);
	return NULL;
}

/*
 * Writeback is asynchronous; poll until at least one writeback has
 * been recorded for @cg, or until @timeout_ms has elapsed.
 */
static long wait_for_writeback(const char *cg, int timeout_ms)
{
	long elapsed, count;
	for (elapsed = 0; elapsed < timeout_ms; elapsed += 100) {
		count = get_cg_wb_count(cg);

		if (count < 0)
			return -1;
		if (count > 0)
			return count;

		usleep(100000);
	}

	return 0;
}

/*
 * Sanity test to check that pages are written into zswap.
 */
static int test_zswap_usage(const char *root)
{
	long zswpout_before, zswpout_after;
	int ret = KSFT_FAIL;
	char *test_group;

	test_group = cg_name(root, "no_shrink_test");
	if (!test_group)
		goto out;
	if (cg_create(test_group))
		goto out;
	if (cg_write(test_group, "memory.max", "1M"))
		goto out;

	zswpout_before = get_zswpout(test_group);
	if (zswpout_before < 0) {
		ksft_print_msg("Failed to get zswpout\n");
		goto out;
	}

	/* Allocate more than memory.max to push memory into zswap */
	if (cg_run(test_group, allocate_bytes, (void *)MB(4)))
		goto out;

	/* Verify that pages come into zswap */
	zswpout_after = get_zswpout(test_group);
	if (zswpout_after <= zswpout_before) {
		ksft_print_msg("zswpout does not increase after test program\n");
		goto out;
	}
	ret = KSFT_PASS;

out:
	cg_destroy(test_group);
	free(test_group);
	return ret;
}

/*
 * Check that when memory.zswap.max = 0, no pages can go to the zswap pool for
 * the cgroup.
 */
static int test_swapin_nozswap(const char *root)
{
	int ret = KSFT_FAIL;
	char *test_group, mem_max_buf[32];
	long swap_peak, zswpout, min_swap;
	size_t allocation_size = page_size * 512;

	min_swap = allocation_size / 4;
	snprintf(mem_max_buf, sizeof(mem_max_buf), "%zu", allocation_size * 3/4);

	test_group = cg_name(root, "no_zswap_test");
	if (!test_group)
		goto out;
	if (cg_create(test_group))
		goto out;
	if (cg_write(test_group, "memory.max", mem_max_buf))
		goto out;
	if (cg_write(test_group, "memory.zswap.max", "0"))
		goto out;

	/* Allocate and read more than memory.max to trigger swapin */
	if (cg_run(test_group, allocate_and_read_bytes, (void *)allocation_size))
		goto out;

	/* Verify that pages are swapped out, but no zswap happened */
	swap_peak = cg_read_long(test_group, "memory.swap.peak");
	if (swap_peak < 0) {
		ksft_print_msg("failed to get cgroup's swap_peak\n");
		goto out;
	}

	if (swap_peak < min_swap) {
		ksft_print_msg("at least %ldKB of memory should be swapped out\n",
				min_swap / 1024);
		goto out;
	}

	zswpout = get_zswpout(test_group);
	if (zswpout < 0) {
		ksft_print_msg("failed to get zswpout\n");
		goto out;
	}

	if (zswpout > 0) {
		ksft_print_msg("zswapout > 0 when memory.zswap.max = 0\n");
		goto out;
	}

	ret = KSFT_PASS;

out:
	cg_destroy(test_group);
	free(test_group);
	return ret;
}

/* Simple test to verify the (z)swapin code paths */
static int test_zswapin(const char *root)
{
	int ret = KSFT_FAIL;
	char *test_group;
	long zswpin;

	test_group = cg_name(root, "zswapin_test");
	if (!test_group)
		goto out;
	if (cg_create(test_group))
		goto out;
	if (cg_write(test_group, "memory.max", "8M"))
		goto out;
	if (cg_write(test_group, "memory.zswap.max", "max"))
		goto out;

	/* Allocate and read more than memory.max to trigger (z)swap in */
	if (cg_run(test_group, allocate_and_read_bytes, (void *)MB(32)))
		goto out;

	zswpin = cg_read_key_long(test_group, "memory.stat", "zswpin ");
	if (zswpin < 0) {
		ksft_print_msg("failed to get zswpin\n");
		goto out;
	}

	if (zswpin < MB(24) / page_size) {
		ksft_print_msg("at least 24MB should be brought back from zswap\n");
		goto out;
	}

	ret = KSFT_PASS;

out:
	cg_destroy(test_group);
	free(test_group);
	return ret;
}

/*
 * Attempt writeback with the following steps:
 * 1. Allocate memory.
 * 2. Reclaim memory equal to the amount that was allocated in step 1.
      This will move it into zswap.
 * 3. Save current zswap usage.
 * 4. Move the memory allocated in step 1 back in from zswap.
 * 5. Set zswap.max to 1/4 of the amount that was recorded in step 3.
 * 6. Attempt to reclaim memory equal to the amount that was allocated,
      this will either trigger writeback if it's enabled, or reclamation
      will fail if writeback is disabled as there isn't enough zswap space.
 */
static int attempt_writeback(const char *cgroup, void *arg)
{
	size_t memsize = page_size * 1024;
	char buf[page_size];
	long zswap_usage;
	bool wb_enabled = *(bool *) arg;
	int ret = -1;
	char *mem;

	mem = (char *)malloc(memsize);
	if (!mem)
		return ret;

	/*
	 * Fill half of each page with increasing data, and keep other
	 * half empty, this will result in data that is still compressible
	 * and ends up in zswap, with material zswap usage.
	 */
	for (int i = 0; i < page_size; i++)
		buf[i] = i < page_size/2 ? (char) i : 0;

	for (int i = 0; i < memsize; i += page_size)
		memcpy(&mem[i], buf, page_size);

	/* Try and reclaim allocated memory */
	if (cg_write_numeric(cgroup, "memory.reclaim", memsize)) {
		ksft_print_msg("Failed to reclaim all of the requested memory\n");
		goto out;
	}

	zswap_usage = cg_read_long(cgroup, "memory.zswap.current");

	/* zswpin */
	for (int i = 0; i < memsize; i += page_size) {
		if (memcmp(&mem[i], buf, page_size)) {
			ksft_print_msg("invalid memory\n");
			goto out;
		}
	}

	if (cg_write_numeric(cgroup, "memory.zswap.max", zswap_usage/4))
		goto out;

	/*
	 * If writeback is enabled, trying to reclaim memory now will trigger a
	 * writeback as zswap.max is 1/4 of what was needed when reclaim ran the first time.
	 * If writeback is disabled, memory reclaim will fail as zswap is limited and
	 * it can't writeback to swap.
	 */
	ret = cg_write_numeric(cgroup, "memory.reclaim", memsize);
	if (!wb_enabled)
		ret = (ret == -EAGAIN) ? 0 : -1;

out:
	free(mem);
	return ret;
}

static int test_zswap_writeback_one(const char *cgroup, bool wb)
{
	long zswpwb_before, zswpwb_after;

	zswpwb_before = get_cg_wb_count(cgroup);
	if (zswpwb_before != 0) {
		ksft_print_msg("zswpwb_before = %ld instead of 0\n", zswpwb_before);
		return -1;
	}

	if (cg_run(cgroup, attempt_writeback, (void *) &wb))
		return -1;

	/* Verify that zswap writeback occurred only if writeback was enabled */
	if (wb)
		zswpwb_after = wait_for_writeback(cgroup, 5000);
	else
		zswpwb_after = get_cg_wb_count(cgroup);
	if (zswpwb_after < 0)
		return -1;

	if (wb != !!zswpwb_after) {
		ksft_print_msg("zswpwb_after is %ld while wb is %s\n",
				zswpwb_after, wb ? "enabled" : "disabled");
		return -1;
	}

	return 0;
}

/* Test to verify the zswap writeback path */
static int test_zswap_writeback(const char *root, bool wb)
{
	int ret = KSFT_FAIL;
	char *test_group, *test_group_child = NULL;

	if (cg_read_strcmp(root, "memory.zswap.writeback", "1"))
		return KSFT_SKIP;

	test_group = cg_name(root, "zswap_writeback_test");
	if (!test_group)
		goto out;
	if (cg_create(test_group))
		goto out;
	if (cg_write(test_group, "memory.zswap.writeback", wb ? "1" : "0"))
		goto out;

	if (test_zswap_writeback_one(test_group, wb))
		goto out;

	/* Reset memory.zswap.max to max (modified by attempt_writeback), and
	 * set up child cgroup, whose memory.zswap.writeback is hardcoded to 1.
	 * Thus, the parent's setting shall be what's in effect. */
	if (cg_write(test_group, "memory.zswap.max", "max"))
		goto out;
	if (cg_write(test_group, "cgroup.subtree_control", "+memory"))
		goto out;

	test_group_child = cg_name(test_group, "zswap_writeback_test_child");
	if (!test_group_child)
		goto out;
	if (cg_create(test_group_child))
		goto out;
	if (cg_write(test_group_child, "memory.zswap.writeback", "1"))
		goto out;

	if (test_zswap_writeback_one(test_group_child, wb))
		goto out;

	ret = KSFT_PASS;

out:
	if (test_group_child) {
		cg_destroy(test_group_child);
		free(test_group_child);
	}
	cg_destroy(test_group);
	free(test_group);
	return ret;
}

static int test_zswap_writeback_enabled(const char *root)
{
	return test_zswap_writeback(root, true);
}

static int test_zswap_writeback_disabled(const char *root)
{
	return test_zswap_writeback(root, false);
}

static bool zswap_shrinker_enabled(void)
{
	char value[2];

	if (read_text(PATH_ZSWAP_SHRINKER_ENABLED, value, sizeof(value)) <= 0)
		return 0;

	return value[0] == 'Y';
}

/*
 * When trying to store a memcg page in zswap, if the memcg hits its memory
 * limit in zswap, writeback should affect only the zswapped pages of that
 * memcg.
 */
static int test_no_invasive_cgroup_shrink(const char *root)
{
	int ret = KSFT_FAIL;
	unsigned int off;
	long zswpwb_before, zswpwb_after, zswpwb_target;
	size_t allocation_size = page_size * 1024;
	unsigned int nr_pages = allocation_size / page_size;
	char zswap_max_buf[32], mem_max_buf[32];
	char *zw_allocation = NULL, *wb_allocation = NULL;
	char *zw_group = NULL, *wb_group = NULL;

	snprintf(zswap_max_buf, sizeof(zswap_max_buf), "%d", page_size);
	snprintf(mem_max_buf, sizeof(mem_max_buf), "%zu", allocation_size / 2);

	wb_group = setup_test_group_1M(root, "per_memcg_wb_test1");
	if (!wb_group)
		return KSFT_FAIL;
	if (cg_write(wb_group, "memory.zswap.max", zswap_max_buf))
		goto out;
	if (cg_write(wb_group, "memory.max", mem_max_buf))
		goto out;

	zw_group = setup_test_group_1M(root, "per_memcg_wb_test2");
	if (!zw_group)
		goto out;
	if (cg_write(zw_group, "memory.max", mem_max_buf))
		goto out;

	/* Push some zw_group memory into zswap (simple data, easy to compress) */
	if (cg_enter_current(zw_group))
		goto out;
	zw_allocation = malloc(allocation_size);
	for (int i = 0; i < nr_pages; i++) {
		off = (unsigned long)i * page_size;
		memset(&zw_allocation[off], 0, page_size);
		memset(&zw_allocation[off], 'a', page_size/4);
	}
	if (cg_read_key_long(zw_group, "memory.stat", "zswapped") < 1)
		goto out;

	/* If the shrinker is enabled, try to let the writebacks finish first */
	if (zswap_shrinker_enabled())
		sleep(5);

	zswpwb_before = get_cg_wb_count(zw_group);
	if (zswpwb_before < 0)
		goto out;

	/* Push wb_group memory into zswap with hard-to-compress data to trigger wb */
	if (cg_enter_current(wb_group))
		goto out;
	wb_allocation = malloc(allocation_size);
	if (!wb_allocation)
		goto out;
	for (int i = 0; i < nr_pages; i++) {
		off = (unsigned long)i * page_size;
		memset(&wb_allocation[off], 0, page_size);
		getrandom(&wb_allocation[off], page_size/4, 0);
	}

	/* Verify that only zswapped memory from wb_group has been written back */
	zswpwb_target = wait_for_writeback(wb_group, 5000);
	zswpwb_after = get_cg_wb_count(zw_group);

	if (zswpwb_target > 0 && zswpwb_before == zswpwb_after)
		ret = KSFT_PASS;

out:
	cg_enter_current(root);
	if (zw_group) {
		cg_destroy(zw_group);
		free(zw_group);
	}
	if (wb_group) {
		cg_destroy(wb_group);
		free(wb_group);
	}
	if (zw_allocation)
		free(zw_allocation);
	if (wb_allocation)
		free(wb_allocation);
	return ret;
}

struct no_kmem_bypass_child_args {
	size_t target_alloc_bytes;
	size_t child_allocated;
};

static int no_kmem_bypass_child(const char *cgroup, void *arg)
{
	struct no_kmem_bypass_child_args *values = arg;
	void *allocation;

	allocation = malloc(values->target_alloc_bytes);
	if (!allocation) {
		values->child_allocated = true;
		return -1;
	}
	for (long i = 0; i < values->target_alloc_bytes; i += page_size)
		((char *)allocation)[i] = 'a';
	values->child_allocated = true;
	pause();
	free(allocation);
	return 0;
}

/*
 * When pages owned by a memcg are pushed to zswap by kswapd, they should be
 * charged to that cgroup. This wasn't the case before commit
 * cd08d80ecdac("mm: correctly charge compressed memory to its memcg").
 *
 * The test first allocates memory in a memcg, then raises min_free_kbytes to
 * a very high value so that the allocation falls below low wm, then makes
 * another allocation to trigger kswapd that should push the memcg-owned pages
 * to zswap and verifies that the zswap pages are correctly charged.
 *
 * To be run on a VM with at most 4G of memory.
 */
static int test_no_kmem_bypass(const char *root)
{
	size_t min_free_kb_high, min_free_kb_low, min_free_kb_original;
	struct no_kmem_bypass_child_args *values;
	size_t trigger_allocation_size;
	int wait_child_iteration = 0;
	long stored_pages_threshold;
	struct sysinfo sys_info;
	int ret = KSFT_FAIL;
	int child_status;
	char *test_group = NULL;
	pid_t child_pid;

	/* Read sys info and compute test values accordingly */
	if (sysinfo(&sys_info) != 0)
		return KSFT_FAIL;
	if (sys_info.totalram > GB(4)) {
		ksft_print_msg(
			"requires less than 4GB total ram, sys_info.totalram: %.1fGB\n",
			(double)sys_info.totalram / GB(1));
		return KSFT_SKIP;
	}
	if (access(PATH_ZSWAP_STORED_PAGES, R_OK)) {
		ksft_print_msg("debugfs not mounted at /sys/kernel/debug\n");
		return KSFT_SKIP;
	}
	values = mmap(0, sizeof(struct no_kmem_bypass_child_args), PROT_READ |
			PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0);
	if (values == MAP_FAILED)
		return KSFT_FAIL;
	if (read_min_free_kb(&min_free_kb_original))
		return KSFT_FAIL;
	min_free_kb_high = sys_info.totalram / 2000;
	min_free_kb_low = sys_info.totalram / 500000;
	values->target_alloc_bytes = (sys_info.totalram - min_free_kb_high * 1000) +
		sys_info.totalram * 5 / 100;
	stored_pages_threshold = sys_info.totalram / 5 / page_size;
	trigger_allocation_size = sys_info.totalram / 20;

	/* Set up test memcg */
	test_group = cg_name(root, "kmem_bypass_test");
	if (!test_group)
		goto out;

	/* Spawn memcg child and wait for it to allocate */
	set_min_free_kb(min_free_kb_low);
	if (cg_create(test_group))
		goto out;
	values->child_allocated = false;
	child_pid = cg_run_nowait(test_group, no_kmem_bypass_child, values);
	if (child_pid < 0)
		goto out;
	while (!values->child_allocated && wait_child_iteration++ < 10000)
		usleep(1000);

	/* Try to wakeup kswapd and let it push child memory to zswap */
	set_min_free_kb(min_free_kb_high);
	for (int i = 0; i < 20; i++) {
		size_t stored_pages;
		char *trigger_allocation = malloc(trigger_allocation_size);

		if (!trigger_allocation)
			break;
		for (int i = 0; i < trigger_allocation_size; i += page_size)
			trigger_allocation[i] = 'b';
		usleep(100000);
		free(trigger_allocation);
		if (get_zswap_stored_pages(&stored_pages))
			break;
		if (stored_pages < 0)
			break;
		/* If memory was pushed to zswap, verify it belongs to memcg */
		if (stored_pages > stored_pages_threshold) {
			int zswapped = cg_read_key_long(test_group, "memory.stat", "zswapped ");
			int delta = stored_pages * page_size - zswapped;
			int result_ok = delta < stored_pages * page_size / 4;

			ret = result_ok ? KSFT_PASS : KSFT_FAIL;
			break;
		}
	}

	kill(child_pid, SIGTERM);
	waitpid(child_pid, &child_status, 0);
out:
	set_min_free_kb(min_free_kb_original);
	cg_destroy(test_group);
	free(test_group);
	return ret;
}

struct incomp_child_args {
	size_t size;
	int pipefd[2];
	int madvise_ret;
	int madvise_errno;
};

static int allocate_random_and_wait(const char *cgroup, void *arg)
{
	struct incomp_child_args *values = arg;
	size_t size = values->size;
	char *mem;
	int fd;
	ssize_t n;

	close(values->pipefd[0]);

	mem = mmap(NULL, size, PROT_READ | PROT_WRITE,
		   MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
	if (mem == MAP_FAILED)
		return -1;

	/* Fill with random data from /dev/urandom - incompressible */
	fd = open("/dev/urandom", O_RDONLY);
	if (fd < 0) {
		munmap(mem, size);
		return -1;
	}

	for (size_t i = 0; i < size; ) {
		n = read(fd, mem + i, size - i);
		if (n <= 0)
			break;
		i += n;
	}
	close(fd);

	/* Touch all pages to ensure they're faulted in */
	for (size_t i = 0; i < size; i += page_size)
		mem[i] = mem[i];

	/* Use MADV_PAGEOUT to push pages into zswap */
	values->madvise_ret = madvise(mem, size, MADV_PAGEOUT);
	values->madvise_errno = errno;

	/* Notify parent that allocation and pageout are done */
	write(values->pipefd[1], "x", 1);
	close(values->pipefd[1]);

	/* Keep memory alive for parent to check stats */
	pause();
	munmap(mem, size);
	return 0;
}

static long get_zswap_incomp(const char *cgroup)
{
	return cg_read_key_long(cgroup, "memory.stat", "zswap_incomp ");
}

/*
 * Test that incompressible pages (random data) are tracked by zswap_incomp.
 *
 * The child process allocates random data within memory.max, then uses
 * MADV_PAGEOUT to push pages into zswap. The parent waits on a pipe for
 * the child to finish, then checks the zswap_incomp stat before the child
 * exits (zswap_incomp is a gauge that decreases on free).
 */
static int test_zswap_incompressible(const char *root)
{
	int ret = KSFT_FAIL;
	struct incomp_child_args *values;
	char *test_group;
	long zswap_incomp;
	pid_t child_pid;
	int child_status;
	char buf;

	values = mmap(0, sizeof(struct incomp_child_args), PROT_READ |
			PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0);
	if (values == MAP_FAILED)
		return KSFT_FAIL;

	if (pipe(values->pipefd)) {
		munmap(values, sizeof(struct incomp_child_args));
		return KSFT_FAIL;
	}

	test_group = cg_name(root, "zswap_incompressible_test");
	if (!test_group)
		goto out;
	if (cg_create(test_group))
		goto out;
	if (cg_write(test_group, "memory.max", "32M"))
		goto out;

	values->size = MB(4);
	child_pid = cg_run_nowait(test_group, allocate_random_and_wait, values);
	if (child_pid < 0)
		goto out;

	close(values->pipefd[1]);

	/* Wait for child to finish allocating and pageout */
	read(values->pipefd[0], &buf, 1);
	close(values->pipefd[0]);

	zswap_incomp = get_zswap_incomp(test_group);
	if (zswap_incomp <= 0) {
		long zswpout = get_zswpout(test_group);
		long zswapped = cg_read_key_long(test_group, "memory.stat", "zswapped ");
		long zswap_b = cg_read_key_long(test_group, "memory.stat", "zswap ");

		ksft_print_msg("zswap_incomp not increased: %ld\n", zswap_incomp);
		ksft_print_msg("debug: zswpout=%ld zswapped=%ld zswap_b=%ld\n",
			       zswpout, zswapped, zswap_b);
		ksft_print_msg("debug: madvise ret=%d errno=%d\n",
			       values->madvise_ret, values->madvise_errno);
		goto out_kill;
	}

	ret = KSFT_PASS;

out_kill:
	kill(child_pid, SIGTERM);
	waitpid(child_pid, &child_status, 0);
out:
	cg_destroy(test_group);
	free(test_group);
	munmap(values, sizeof(struct incomp_child_args));
	return ret;
}

#define T(x) { x, #x }
struct zswap_test {
	int (*fn)(const char *root);
	const char *name;
} tests[] = {
	T(test_zswap_usage),
	T(test_swapin_nozswap),
	T(test_zswapin),
	T(test_zswap_writeback_enabled),
	T(test_zswap_writeback_disabled),
	T(test_no_kmem_bypass),
	T(test_no_invasive_cgroup_shrink),
	T(test_zswap_incompressible),
};
#undef T

static void check_zswap_enabled(void)
{
	char value[2];

	if (access(PATH_ZSWAP, F_OK))
		ksft_exit_skip("zswap isn't configured\n");

	if (read_text(PATH_ZSWAP_ENABLED, value, sizeof(value)) <= 0)
		ksft_exit_fail_msg("Failed to read " PATH_ZSWAP_ENABLED "\n");

	if (value[0] == 'N')
		ksft_exit_skip("zswap is disabled (hint: echo 1 > " PATH_ZSWAP_ENABLED ")\n");
}

int main(int argc, char **argv)
{
	char root[PATH_MAX];
	int i;

	page_size = sysconf(_SC_PAGE_SIZE);
	if (page_size <= 0)
		page_size = BUF_SIZE;

	ksft_print_header();
	if (cg_find_unified_root(root, sizeof(root), NULL))
		ksft_exit_skip("cgroup v2 isn't mounted\n");

	check_zswap_enabled();

	/*
	 * Check that memory controller is available:
	 * memory is listed in cgroup.controllers
	 */
	if (cg_read_strstr(root, "cgroup.controllers", "memory"))
		ksft_exit_skip("memory controller isn't available\n");

	if (cg_read_strstr(root, "cgroup.subtree_control", "memory"))
		if (cg_write(root, "cgroup.subtree_control", "+memory"))
			ksft_exit_skip("Failed to set memory controller\n");

	ksft_set_plan(ARRAY_SIZE(tests));
	for (i = 0; i < ARRAY_SIZE(tests); i++) {
		switch (tests[i].fn(root)) {
		case KSFT_PASS:
			ksft_test_result_pass("%s\n", tests[i].name);
			break;
		case KSFT_SKIP:
			ksft_test_result_skip("%s\n", tests[i].name);
			break;
		default:
			ksft_test_result_fail("%s\n", tests[i].name);
			break;
		}
	}

	ksft_finished();
}