ksmctl from rhel ksm packages with added default params support

ksm.sysconfig

# The maximum number of unswappable kernel pages
# which may be allocated by ksm (0 for unlimited)
# If unset, defaults to half of total memory
# KSM_MAX_KERNEL_PAGES=
# KSM_SLEEP_MSECS=20
# KSM_PAGES_TO_SCAN=100
# KSM_MERGE_ACROSS_NODES=1
# KSM_MAX_PAGE_SHARING=256
# KSM_USE_ZERO_PAGES=0

ksmctl.c

/* Start/stop KSM, for systemd.
 * Copyright (C) 2009, 2011 Red Hat, Inc.
 * Written by Paolo Bonzini <pbonzini@redhat.com>.
 * Based on the original sysvinit script by Dan Kenigsberg <danken@redhat.com>
 * This file is distributed under the GNU General Public License, version 2
 * or later.  */

#include <unistd.h>
#include <stdio.h>
#include <limits.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>

#define KSM_MAX_KERNEL_PAGES_FILE   "/sys/kernel/mm/ksm/max_kernel_pages"
#define KSM_RUN_FILE		 	          "/sys/kernel/mm/ksm/run"
#define KSM_PAGES_TO_SCAN_FILE	    "/sys/kernel/mm/ksm/pages_to_scan"
#define KSM_SLEEP_MSECS_FILE	      "/sys/kernel/mm/ksm/sleep_millisecs"
#define KSM_MERGE_ACROSS_NODES_FILE "/sys/kernel/mm/ksm/merge_across_nodes"
#define KSM_MAX_PAGE_SHARING_FILE	  "/sys/kernel/mm/ksm/max_page_sharing"
#define KSM_USE_ZERO_PAGES_FILE	   	"/sys/kernel/mm/ksm/use_zero_pages"

char *program_name;

int usage(void)
{
	fprintf(stderr, "Usage: %s {start|stop}\n", program_name);
	return 1;
}

int write_value(uint64_t value, char *filename)
{
	FILE *fp;
	if (!(fp = fopen(filename, "w")) ||
	    fprintf(fp, "%llu\n", (unsigned long long) value) == EOF ||
	    fflush(fp) == EOF ||
	    fclose(fp) == EOF)
		return 1;

	return 0;
}

uint64_t ksm_max_kernel_pages()
{
	char *var = getenv("KSM_MAX_KERNEL_PAGES");
	char *endptr;
	uint64_t value;
	if (var && *var) {
		value = strtoll(var, &endptr, 0);
		if (value < LLONG_MAX && !*endptr)
			return value;
	}
	/* Unless KSM_MAX_KERNEL_PAGES is set, let KSM munch up to half of
	 * total memory.  */
	return sysconf(_SC_PHYS_PAGES) / 2;
}


uint64_t ksm_by_unsigned_int(char *env_name, uint64_t default_value){
	char *var = getenv(env_name);
	char *endptr;
	uint64_t value;
	if (var && *var) {
		value = strtoll(var, &endptr, 0);
		if (value < UINT_MAX && !*endptr)
			return value;
	}
	return default_value;
}

uint64_t ksm_by_int(char *env_name, uint64_t default_value){
	char *var = getenv(env_name);
	char *endptr;
	uint64_t value;
	if (var && *var) {
		value = strtoll(var, &endptr, 0);
		if (value < INT_MAX && !*endptr)
			return value;
	}
	return default_value;
}

int start(void)
{
	if (access(KSM_MAX_KERNEL_PAGES_FILE, R_OK) >= 0)
		write_value(ksm_max_kernel_pages(), KSM_MAX_KERNEL_PAGES_FILE);

	/* Milliseconds ksmd should sleep between batches
	 * static unsigned int ksm_thread_sleep_millisecs = 20; 
	 */
	if (getenv("KSM_SLEEP_MSECS") && access(KSM_SLEEP_MSECS_FILE, R_OK) >= 0)
		write_value(ksm_by_unsigned_int("KSM_SLEEP_MSECS", 20), KSM_SLEEP_MSECS_FILE);

	/* Number of pages ksmd should scan in one batch 
	 * static unsigned int ksm_thread_pages_to_scan = 100;
	 */
	if (getenv("KSM_PAGES_TO_SCAN") && access(KSM_PAGES_TO_SCAN_FILE, R_OK) >= 0)
		write_value(ksm_by_unsigned_int("KSM_PAGES_TO_SCAN", 100), KSM_PAGES_TO_SCAN_FILE);

	/* Zeroed when merging across nodes is not allowed 
	 * static unsigned int ksm_merge_across_nodes = 1;
	*/
	if (getenv("KSM_MERGE_ACROSS_NODES") && access(KSM_PAGES_TO_SCAN_FILE, R_OK) >= 0)
		write_value(ksm_by_unsigned_int("KSM_MERGE_ACROSS_NODES", 1), KSM_MERGE_ACROSS_NODES_FILE);

	/* Maximum number of page slots sharing a stable node
	 * static int ksm_max_page_sharing = 256; 
	 */
	if (getenv("KSM_MAX_PAGE_SHARING") && access(KSM_PAGES_TO_SCAN_FILE, R_OK) >= 0)
		write_value(ksm_by_int("KSM_MAX_PAGE_SHARING", 256), KSM_MAX_PAGE_SHARING_FILE);

	/* Whether to merge empty (zeroed) pages with actual zero pages
	 * Default to false for backwards compatibility
	 * ksm_use_zero_pages = false;
	 */
	if (getenv("KSM_USE_ZERO_PAGES") && access(KSM_PAGES_TO_SCAN_FILE, R_OK) >= 0)
		write_value(ksm_by_unsigned_int("KSM_USE_ZERO_PAGES", 0), KSM_USE_ZERO_PAGES_FILE);

	return write_value(1, KSM_RUN_FILE);
}

int stop(void)
{
	return write_value(0, KSM_RUN_FILE);
}

int main(int argc, char **argv)
{
	program_name = argv[0];
	if (argc < 2) {
		return usage();
	} else if (!strcmp(argv[1], "start")) {
		return start();
	} else if (!strcmp(argv[1], "stop")) {
		return stop();
	} else {
		return usage();
	}
}

Comments and default value were gotten from ./mm/kms.c file from 4.13 kernel.