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--- realtime:documentation:howto:applications:memory:mlockall_globals_sample [2017/06/08 17:26]
jithu
+++ realtime:documentation:howto:applications:memory:mlockall_globals_sample [2017/06/10 00:28] (current)
jithu
@@ Line 3: / Line 3: @@
 <code c>
-/* This application checks whether mlockall() forces all pages of a
+/*
+ * # gcc -o check_global  check_global.c -Wall -O3
+ * # ./check_global
+ * # ./check_global -nolockmem  (will cause faults)
+ * This application checks whether mlockall() forces all pages of a
  * global array into RAM. Normally, the OS maps a 'copy on write' MMU page
  * to such arrays meaning that reading from the array returns only zeros and
@@ Line 10: / Line 14: @@
  */
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
-#include <unistd.h>
 #include <sys/mman.h>
 #include <sys/resource.h>
+#include <unistd.h>
+/* Define the global array*/
+#define  NUM_PAGES 5000
+#define  PAGE_SZ  (1024 * 4)  /* Assume 4kb pages*/
+char glob_buffer[NUM_PAGES * PAGE_SZ];
 /* Lock the application in memory to avoid page faults*/
-static void lockApplication(void)
+static void lock_application(void)
 {
-	if (mlockall(MCL_CURRENT | MCL_FUTURE) != 0 )
+	if (mlockall(MCL_CURRENT | MCL_FUTURE) != 0) {
-	{
+		perror("mlockall() failed - root ?");
-	    perror( "mlockall() failed" );
+		exit(-1);
 	}
 }
-/* Dump minor and major page faults that occurred since the previous call*/
+/* Dump minor and major page faults that occurred since the previous call */
-static bool dumpPageFaults(void)
+static int dump_page_faults(void)
 {
-	bool l_PageFaultsDetected = false;
+	int			new_minor_page_faults, new_major_page_faults;
-	static bool ls_Init = false;
+	int			page_faults_detected = 0;
-	static struct rusage ls_RusagePrevious;
+	static struct rusage	rusage_prev;
-	struct rusage l_Rusage;
+	static int		init;
+	struct rusage		rusage;
-	getrusage(RUSAGE_SELF, &l_Rusage);
-	int a_NewMinorPageFaults = l_Rusage.ru_minflt - ls_RusagePrevious.ru_minflt;
+	getrusage(RUSAGE_SELF, &rusage);
-	int a_NewMajorPageFaults = l_Rusage.ru_majflt - ls_RusagePrevious.ru_majflt;
+	new_minor_page_faults = rusage.ru_minflt - rusage_prev.ru_minflt;
-	ls_RusagePrevious.ru_minflt = l_Rusage.ru_minflt;
+	new_major_page_faults = rusage.ru_majflt - rusage_prev.ru_majflt;
-	ls_RusagePrevious.ru_majflt = l_Rusage.ru_majflt;
+	rusage_prev.ru_minflt = rusage.ru_minflt;
+	rusage_prev.ru_majflt = rusage.ru_majflt;
-	if (ls_Init)
-	{
+	if (init) {
-		if ((a_NewMinorPageFaults > 0) || (a_NewMajorPageFaults > 0))
+		if ((new_minor_page_faults > 0) ||
-		{
+		    (new_major_page_faults > 0)) {
-			printf ("New minor/major page faults: %d/%d\n",
+			printf("New minor/major page faults: %d/%d\n",
-				a_NewMinorPageFaults,
+			       new_minor_page_faults, new_major_page_faults);
-				a_NewMajorPageFaults);
+			page_faults_detected = 1;
-			l_PageFaultsDetected = true;
 		}
 	}
-	ls_Init = true;
+	init = 1;
-	return l_PageFaultsDetected;
+	return page_faults_detected;
 }
-/* Define the global array*/
-const static int gs_BufferPages = 5000;
-const static int gs_PageSize = 1024*4; /* Assume 4kb pages*/
-static char gs_Buffer[gs_BufferPages*gs_PageSize];
 int main(int argc, char *argv[])
 {
-	bool l_LockMemory = true;
+	int unexpected_pagefaults_detected;
+	int lock_memory = 1;
+	int buff_value;
 	int i;
-	for (i=1; i<argc; i++)
-	{
+	for (i = 1; i < argc; i++) {
-		if (strncmp (argv[i], "-nolockmem", 10) == 0)
+		if (strncmp(argv[i], "-nolockmem", 10) == 0) {
-		{
 			/* Results in many page faults! */
-			l_LockMemory = false;
+			lock_memory = 0;
 		}
 	}
-	if (l_LockMemory)
+	if (lock_memory) {
-	{
+		lock_application();
-		lockApplication();
+		printf("Current and future memory locked in RAM\n");
-		printf ("Current and future memory locked in RAM\n");
 	}
-	(void)dumpPageFaults(); /* Set the baseline*/
+	(void)dump_page_faults(); /* Set the baseline*/
-	/* printf something so we avoid introducing a page fault simply by performing
+	/* From this point onwards we no longer expect any page faults */
-	 * the potentially first printf call.
+	unexpected_pagefaults_detected = 0;
-	 */
-	const int l_PageSize = sysconf(_SC_PAGESIZE);
+	for (i = 0; i < NUM_PAGES; i++) {
-	printf ("Page size = %d\n", l_PageSize);
+		buff_value = (int) (glob_buffer[i * PAGE_SZ]);
-	(void)dumpPageFaults();
+		if (buff_value != 0) {
+			printf("Reading unexpected value %d on page %d of global buffer.\n",
-	/* From this point onwards we no longer expect to have any page faults.*/
+				 buff_value, i);
-	bool l_UnexpectedPageFaultsDetected = false;
-	for (i=0; i<gs_BufferPages; i++)
-	{
-		int l_Value = static_cast<int>(gs_Buffer[i*gs_PageSize]);
-		if (l_Value != 0)
-		{
-			printf ("Reading unexpected value %d on page %d of static buffer.\n",
-				l_Value,
-				i);
-		}
-		if (dumpPageFaults())
-		{
-			l_UnexpectedPageFaultsDetected = true;
 		}
-		gs_Buffer[(i*gs_PageSize)+1] = 1;
+		if (dump_page_faults())
-		if (dumpPageFaults())
+			unexpected_pagefaults_detected = 1;
-		{
-			printf ("Writing to page %d of static buffer caused page fault(s)\n", i);
+		glob_buffer[(i * PAGE_SZ) + 1] = 1;
-			l_UnexpectedPageFaultsDetected = true;
+		if (dump_page_faults()) {
+			printf("Writing to page %d of global buffer caused page fault(s)\n",
+					 i);
+			unexpected_pagefaults_detected = 1;
 		}
 	}
-	printf ("Done, result: %s\n",
+	printf("Done, result: %s\n",
-		l_UnexpectedPageFaultsDetected ? "failed":"success");
+		unexpected_pagefaults_detected ? "failed" : "success");
-	return (l_UnexpectedPageFaultsDetected ? 1:0);
+	return unexpected_pagefaults_detected ? 1 : 0;
 }
 </code>

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