[PATCH] update overcommit doc and comment

Update Doc and remove FIXME comment from fork.c now accounting right.

Documentation/vm/overcommit-accounting

@@ -37,13 +37,13 @@ How It Works
 The overcommit is based on the following rules
 
 For a file backed map
-	SHARED or READ only	-	0 cost (the file is the map not swap)
+	SHARED or READ-only	-	0 cost (the file is the map not swap)
+	PRIVATE WRITABLE	-	size of mapping per instance
 
-	WRITABLE SHARED		-	size of mapping per instance
-
-For a direct map
-	SHARED or READ only	-	size of mapping
-	PRIVATE WRITEABLE	-	size of mapping per instance
+For an anonymous or /dev/zero map
+	SHARED			-	size of mapping
+	PRIVATE READ-only	-	0 cost (but of little use)
+	PRIVATE WRITABLE	-	size of mapping per instance
 
 Additional accounting
 	Pages made writable copies by mmap
@@ -66,5 +66,3 @@ o	Implement actual limit enforcement
 To Do
 -----
 o	Account ptrace pages (this is hard)
-o	Account for shared anonymous mappings properly
-	- right now we account them per instance

kernel/fork.c

@@ -210,17 +210,12 @@ static inline int dup_mmap(struct mm_struct * mm)
 		retval = -ENOMEM;
 		if(mpnt->vm_flags & VM_DONTCOPY)
 			continue;
-
-		/*
-		 * FIXME: shared writable map accounting should be one off
-		 */
 		if (mpnt->vm_flags & VM_ACCOUNT) {
 			unsigned int len = (mpnt->vm_end - mpnt->vm_start) >> PAGE_SHIFT;
 			if (!vm_enough_memory(len))
 				goto fail_nomem;
 			charge += len;
 		}
-
 		tmp = kmem_cache_alloc(vm_area_cachep, SLAB_KERNEL);
 		if (!tmp)
 			goto fail_nomem;