mapper4.c
dougm (Doug Moore)
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	dougm
	May 31 2019, 7:38 AM

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mapper4.c
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	#include <sys/mman.h>
	#include <sys/time.h>
	#include <stdlib.h>
	#include <stdio.h>

	enum {MAX_MAPS = 16384, PAGE_SIZE = 4096 };

	int main(int argc, const char *argv[])
	{
	int i;
	int nmappings = 0;
	void *mappings[MAX_MAPS];
	struct timeval beg, end;
	struct timezone tz = {0, 0};

	if (argc >= 2)
	srandom(atoi(argv[1]));

	for (i = 0; i < MAX_MAPS; ++i)
	mappings[i] = MAP_FAILED;

	gettimeofday(&beg, &tz);
	for (i = 0; i < 2048 * MAX_MAPS; ++i) {
	long r = random() % MAX_MAPS;
	if (mappings[r] == MAP_FAILED) {
	mappings[r] = mmap(0, 3*PAGE_SIZE, PROT_WRITE, MAP_ALIGNED(14) \| MAP_ANON, -1, 0);
	if (mappings[r] != MAP_FAILED)
	++nmappings;
	} else {
	munmap(mappings[r], 3*PAGE_SIZE);
	mappings[r] = MAP_FAILED;
	--nmappings;
	}
	}
	gettimeofday(&end, &tz);
	end.tv_sec -= beg.tv_sec;
	end.tv_usec -= beg.tv_usec;
	if (end.tv_usec < 0) {
	end.tv_usec += 1000000;
	end.tv_sec--;
	}
	printf("nmappings = %d, time %ld.%ld; ok?\n", nmappings,
	(long)end.tv_sec, (long)end.tv_usec);
	return 0;
	}