[PATCH] overcommit symbolic constants

Played a bit with overcommit the past hour.

Am not entirely satisfied with the no overcommit mode 2 -
programs segfault when the system is close to that boundary.
So, instead of the somewhat larger patch that I planned to send,
just symbolic names for the modes.

Documentation/vm/overcommit-accounting

-The Linux kernel supports three overcommit handling modes
+The Linux kernel supports the following overcommit handling modes
 
 0	-	Heuristic overcommit handling. Obvious overcommits of
 		address space are refused. Used for a typical system. It
@@ -7,10 +7,10 @@ The Linux kernel supports three overcommit handling modes
 		allocate slighly more memory in this mode. This is the 
 		default.
 
-1	-	No overcommit handling. Appropriate for some scientific
+1	-	Always overcommit. Appropriate for some scientific
 		applications.
 
-2	-	(NEW) strict overcommit. The total address space commit
+2	-	Don't overcommit. The total address space commit
 		for the system is not permitted to exceed swap + a
 		configurable percentage (default is 50) of physical RAM.
 		Depending on the percentage you use, in most situations
@@ -27,7 +27,7 @@ Gotchas
 
 The C language stack growth does an implicit mremap. If you want absolute
 guarantees and run close to the edge you MUST mmap your stack for the 
-largest size you think you will need. For typical stack usage is does
+largest size you think you will need. For typical stack usage this does
 not matter much but it's a corner case if you really really care
 
 In mode 2 the MAP_NORESERVE flag is ignored. 

arch/arm/mm/init.c

@@ -590,7 +590,7 @@ void __init mem_init(void)
 		 * anywhere without overcommit, so turn
 		 * it on by default.
 		 */
-		sysctl_overcommit_memory = 1;
+		sysctl_overcommit_memory = OVERCOMMIT_ALWAYS;
 	}
 }
 

arch/arm26/mm/init.c

@@ -376,7 +376,7 @@ void __init mem_init(void)
 	 * Turn on overcommit on tiny machines
 	 */
 	if (PAGE_SIZE >= 16384 && num_physpages <= 128) {
-		sysctl_overcommit_memory = 1;
+		sysctl_overcommit_memory = OVERCOMMIT_ALWAYS;
 		printk("Turning on overcommit\n");
 	}
 }

include/linux/mman.h

@@ -10,6 +10,9 @@
 #define MREMAP_MAYMOVE	1
 #define MREMAP_FIXED	2
 
+#define OVERCOMMIT_GUESS		0
+#define OVERCOMMIT_ALWAYS		1
+#define OVERCOMMIT_NEVER		2
 extern int sysctl_overcommit_memory;
 extern int sysctl_overcommit_ratio;
 extern atomic_t vm_committed_space;

mm/mmap.c

@@ -54,7 +54,7 @@ pgprot_t protection_map[16] = {
 	__S000, __S001, __S010, __S011, __S100, __S101, __S110, __S111
 };
 
-int sysctl_overcommit_memory = 0;	/* default is heuristic overcommit */
+int sysctl_overcommit_memory = OVERCOMMIT_GUESS;  /* heuristic overcommit */
 int sysctl_overcommit_ratio = 50;	/* default is 50% */
 int sysctl_max_map_count = DEFAULT_MAX_MAP_COUNT;
 atomic_t vm_committed_space = ATOMIC_INIT(0);
@@ -907,7 +907,7 @@ unsigned long do_mmap_pgoff(struct file * file, unsigned long addr,
 		return -ENOMEM;
 
 	if (accountable && (!(flags & MAP_NORESERVE) ||
-			sysctl_overcommit_memory > 1)) {
+			    sysctl_overcommit_memory == OVERCOMMIT_NEVER)) {
 		if (vm_flags & VM_SHARED) {
 			/* Check memory availability in shmem_file_setup? */
 			vm_flags |= VM_ACCOUNT;

mm/nommu.c

@@ -30,7 +30,7 @@ unsigned long max_mapnr;
 unsigned long num_physpages;
 unsigned long askedalloc, realalloc;
 atomic_t vm_committed_space = ATOMIC_INIT(0);
-int sysctl_overcommit_memory; /* default is heuristic overcommit */
+int sysctl_overcommit_memory = OVERCOMMIT_GUESS; /* heuristic overcommit */
 int sysctl_overcommit_ratio = 50; /* default is 50% */
 
 int sysctl_max_map_count = DEFAULT_MAX_MAP_COUNT;

security/commoncap.c

@@ -314,10 +314,10 @@ int cap_vm_enough_memory(long pages)
 	/*
 	 * Sometimes we want to use more memory than we have
 	 */
-	if (sysctl_overcommit_memory == 1)
+	if (sysctl_overcommit_memory == OVERCOMMIT_ALWAYS)
 		return 0;
 
-	if (sysctl_overcommit_memory == 0) {
+	if (sysctl_overcommit_memory == OVERCOMMIT_GUESS) {
 		unsigned long n;
 
 		free = get_page_cache_size();

security/dummy.c

@@ -121,10 +121,10 @@ static int dummy_vm_enough_memory(long pages)
 	/*
 	 * Sometimes we want to use more memory than we have
 	 */
-	if (sysctl_overcommit_memory == 1)
+	if (sysctl_overcommit_memory == OVERCOMMIT_ALWAYS)
 		return 0;
 
-	if (sysctl_overcommit_memory == 0) {
+	if (sysctl_overcommit_memory == OVERCOMMIT_GUESS) {
 		free = get_page_cache_size();
 		free += nr_free_pages();
 		free += nr_swap_pages;

security/selinux/hooks.c

@@ -1554,10 +1554,10 @@ static int selinux_vm_enough_memory(long pages)
         /*
 	 * Sometimes we want to use more memory than we have
 	 */
-	if (sysctl_overcommit_memory == 1)
+	if (sysctl_overcommit_memory == OVERCOMMIT_ALWAYS)
 		return 0;
 
-	if (sysctl_overcommit_memory == 0) {
+	if (sysctl_overcommit_memory == OVERCOMMIT_GUESS) {
 		free = get_page_cache_size();
 		free += nr_free_pages();
 		free += nr_swap_pages;