malloc does not return null when out of memory

[Chuck Swiger]

Kris Kennaway wrote:
> On Wed, Jul 23, 2003 at 11:44:11PM -0400, Mike Tancsa wrote:
[ ... ]
>>> Ah, the annual "memory overcommit" thread.  I thought we were overdue
>>> for one.
>>
>> But why does the man page for malloc (3) say,
>>
>>    If malloc() fails, a NULL pointer is returned.
> 
> Words fail me.

Don't worry about it; you've still got sarcasm to fall back on.  :-)

I don't think the following is a particularly good idea, as the existing prezero 
  ('Z') or junk ('J') options will also serve to reference memory and prevent 
the "memory overcommit issue", but:

22-sec# diff -du malloc.c_old malloc.c
--- malloc.c_old        Thu Jul 24 10:36:43 2003
+++ malloc.c    Thu Jul 24 10:49:41 2003
@@ -229,6 +229,9 @@
  /* junk fill ?  */
  static int malloc_junk;

+/* write a single byte per page to disable overcommit behavior */
+static int malloc_overcommit;
+
  #ifdef HAS_UTRACE

  /* utrace ?  */
@@ -418,6 +421,8 @@
                 case 'R': malloc_realloc = 1; break;
                 case 'j': malloc_junk    = 0; break;
                 case 'J': malloc_junk    = 1; break;
+                case 'o': malloc_overcommit = 0; break
+                case 'O': malloc_overcommit = 1; break
  #ifdef HAS_UTRACE
                 case 'u': malloc_utrace  = 0; break;
                 case 'U': malloc_utrace  = 1; break;
@@ -705,6 +710,7 @@
  imalloc(size_t size)
  {
      void *result;
+    int stride;

      if (suicide)
         abort();
@@ -716,8 +722,13 @@
      else
         result =  malloc_pages(size);

-    if (malloc_zero && result)
-       memset(result, 0, size);
+    if (result) {
+        if (malloc_zero)
+           memset(result, 0, size);
+        else if (malloc_overcommit)
+           for (stride = 0; stride <= size; stride += malloc_pagesize)
+             ((char *)result)[stride] = SOME_JUNK;
+    }

      return result;
  }


-- 
-Chuck