vmfill: portable way to manage the size of the available vm

diff --git a/vmfill.c b/vmfill.c
new file mode 100644 (file)
index 0000000..a7f0a15
--- /dev/null
+++ b/vmfill.c
@@ -0,0 +1,71 @@
+#include <stdlib.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <sys/mman.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#ifndef PAGE_SIZE
+       #define PAGE_SIZE sysconf(_SC_PAGE_SIZE)
+#endif
+
+static void printvm() {
+       int fd = open("/proc/self/smaps", O_RDONLY);
+       char buf[4096];
+       int n;
+
+       printf("/proc/self/smaps:\n");
+       fflush(stdout);
+       while ((n = read(fd, buf, sizeof buf)) > 0)
+               write(1, buf, n);
+       close(fd);
+}
+
+static size_t mmapmax(int fd, void **p) {
+       size_t i,j,n=0;
+
+       for (i=j=SIZE_MAX/2+1; i>=PAGE_SIZE; i/=2) {
+               if ((*p=mmap(NULL, j, PROT_NONE, MAP_PRIVATE, fd, 0)) == MAP_FAILED)
+                       j -= i/2;
+               else {
+                       n = j;
+                       munmap(*p, n);
+                       j += i/2;
+               }
+       }
+       if (n && (*p=mmap(NULL, n, PROT_NONE, MAP_PRIVATE, fd, 0)) == MAP_FAILED) {
+               fprintf(stderr, "failed to mmap the same amount again.\n");
+               exit(1);
+       }
+       return n;
+}
+
+int main(int argc, char *argv[]) {
+       const int fd = open("/dev/zero", O_RDWR);
+       void *p[100];
+       size_t n[100];
+       size_t sum = 0;
+       int i;
+       int vmmaps = 0;
+
+       if (argc == 2 && argv[1][0]=='-' && argv[1][1]=='v')
+               vmmaps = 1;
+
+       for (i=0; i<sizeof p/sizeof *p; i++) {
+               n[i] = mmapmax(fd, p+i);
+               if (!n[i])
+                       break;
+               sum += n[i];
+               printf("%d %16zu B %012zx-%012zx\n", i, n[i], (size_t)p[i], (size_t)p[i]+n[i]);
+       }
+       printf("mmaped %zu B in %d blocks.\n", sum, i);
+
+       printf("try malloc:");
+       for(i=0; i < 1000 && malloc(PAGE_SIZE) != NULL; i++)
+               printf(".");
+       printf(" %zu B\n", i*(size_t)PAGE_SIZE);
+
+       if (vmmaps)
+               printvm();
+       return 0;
+}