* Set a default maximum memory usage value to avoid excessive swapping.

doc/zzuf.1

@@ -159,8 +159,12 @@ untouched.
 \fB\-M\fR, \fB\-\-max\-memory\fR=\fImebibytes\fR
 Specify the maximum amount of memory, in mebibytes (1 MiB = 1,048,576 bytes),
 that children are allowed to allocate. This is useful to detect infinite loops
-that eat up a lot of memory. The value should be set reasonably high so as not
-to interfer with normal program operation.
+that eat up a lot of memory.
+
+The value should be set reasonably high so as not to interfer with normal
+program operation. By default, it is set to 1024 MiB in order to avoid
+accidental excessive swapping. To disable the limitation, set the maximum
+memory usage to -1 instead.
 
 \fBzzuf\fR uses the \fBsetrlimit\fR() call to set memory usage limitations and
 relies on the operating system's ability to enforce such limitations.

src/libzzuf.h

@@ -31,6 +31,10 @@
 #define MIN_RATIO 0.00000000001
 #define MAX_RATIO 5.0
 
+/* The default maximum memory usage is 1024 MiB. If this value is not set,
+ * zzuf may bring a machine down to its knees because of I/O. */
+#define DEFAULT_MEM 1024
+
 struct fuzz
 {
     uint32_t seed;

src/opts.c

@@ -43,7 +43,7 @@ void _zz_opts_init(struct opts *opts)
     opts->md5 = 0;
     opts->checkexit = 0;
     opts->verbose = 0;
-    opts->maxmem = -1;
+    opts->maxmem = DEFAULT_MEM;
     opts->maxtime = -1;
     opts->maxcpu = -1;
     opts->delay = 0;

src/zzuf.c

@@ -1207,7 +1207,7 @@ static void usage(void)
     printf("  -l, --list <list>         only fuzz Nth descriptor with N in <list>\n");
     printf("  -m, --md5                 compute the output's MD5 hash\n");
 #if defined HAVE_SETRLIMIT && defined ZZUF_RLIMIT_MEM
-    printf("  -M, --max-memory <n>      maximum child virtual memory size in MB\n");
+    printf("  -M, --max-memory <n>      maximum child virtual memory in MiB (default %u)\n", DEFAULT_MEM);
 #endif
     printf("  -n, --network             fuzz network input\n");
     printf("  -p, --ports <list>        only fuzz network destination ports in <list>\n");