madvise tests

no-madvise.c

niedbalski@theos-mobile:~$ cat test-madvise.c 
#include <sys/mman.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>


int main(void) {
	size_t size = sysconf(_SC_PAGE_SIZE) * 6; //24K

	void *two_pages =  mmap(NULL, size,
                           PROT_READ | PROT_EXEC | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS,
                           -1, 0);

	memset(two_pages, 0, size);
	//madvise(two_pages, size, MADV_MERGEABLE);

	for(;;) {}

	munmap(two_pages, size);

	return 0;
}

niedbalski@theos-mobile:~$ cat /sys/kernel/mm/ksm/pages_shared 
0
niedbalski@theos-mobile:~$ pmap $(pgrep madvise) | grep rwx
00007fe681a76000     24K rwx--   [ anon ]

niedbalski@theos-mobile:~$ cat /proc/$(pgrep madvise)/status | grep VmPTE
VmPTE:	      24 kB

with-madvise.c

niedbalski@theos-mobile:~$ cat test-madvise.c 
#include <sys/mman.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>


int main(void) {
	size_t size = sysconf(_SC_PAGE_SIZE) * 6; //24K

	void *two_pages =  mmap(NULL, size,
                           PROT_READ | PROT_EXEC | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS,
                           -1, 0);

	memset(two_pages, 0, size);
	madvise(two_pages, size, MADV_MERGEABLE);

	for(;;) {}

	munmap(two_pages, size);

	return 0;
}

niedbalski@theos-mobile:~$ cat /sys/kernel/mm/ksm/pages_shared 
1

niedbalski@theos-mobile:~$ pmap $(pgrep madvise) | grep rwx
00007fa7fea9a000     24K rwx--   [ anon ]

niedbalski@theos-mobile:~$ cat /proc/$(pgrep madvise)/status | grep VmPTE
VmPTE:	      28 kB