[PATCH] factor free memory into max_sane_readahead()

max_sane_readahead() permits the user to readahead up to
half-the-inactive-list's worth of pages.  Which is totally wrong if most of
memory is free.

So make the limit be

	(nr_inactive + nr_free) / 2

fs/proc/proc_misc.c

@@ -140,9 +140,10 @@ static int meminfo_read_proc(char *page, char **start, off_t off,
 	struct page_state ps;
 	unsigned long inactive;
 	unsigned long active;
+	unsigned long free;
 
 	get_page_state(&ps);
-	get_zone_counts(&active, &inactive);
+	get_zone_counts(&active, &inactive, &free);
 
 /*
  * display in kilobytes.

include/linux/mmzone.h

@@ -193,7 +193,8 @@ typedef struct pglist_data {
 extern int numnodes;
 extern struct pglist_data *pgdat_list;
 
-void get_zone_counts(unsigned long *active, unsigned long *inactive);
+void get_zone_counts(unsigned long *active, unsigned long *inactive,
+			unsigned long *free);
 void build_all_zonelists(void);
 void wakeup_kswapd(struct zone *zone);
 

mm/page_alloc.c

@@ -776,15 +776,18 @@ void get_full_page_state(struct page_state *ret)
 	__get_page_state(ret, sizeof(*ret) / sizeof(unsigned long));
 }
 
-void get_zone_counts(unsigned long *active, unsigned long *inactive)
+void get_zone_counts(unsigned long *active,
+		unsigned long *inactive, unsigned long *free)
 {
 	struct zone *zone;
 
 	*active = 0;
 	*inactive = 0;
+	*free = 0;
 	for_each_zone(zone) {
 		*active += zone->nr_active;
 		*inactive += zone->nr_inactive;
+		*free += zone->free_pages;
 	}
 }
 
@@ -838,6 +841,7 @@ void show_free_areas(void)
 	int cpu, temperature;
 	unsigned long active;
 	unsigned long inactive;
+	unsigned long free;
 	struct zone *zone;
 
 	for_each_zone(zone) {
@@ -863,7 +867,7 @@ void show_free_areas(void)
 	}
 
 	get_page_state(&ps);
-	get_zone_counts(&active, &inactive);
+	get_zone_counts(&active, &inactive, &free);
 
 	printk("\nFree pages: %11ukB (%ukB HighMem)\n",
 		K(nr_free_pages()),

mm/readahead.c

@@ -477,7 +477,8 @@ unsigned long max_sane_readahead(unsigned long nr)
 {
 	unsigned long active;
 	unsigned long inactive;
+	unsigned long free;
 
-	get_zone_counts(&active, &inactive);
-	return min(nr, inactive / 2);
+	get_zone_counts(&active, &inactive, &free);
+	return min(nr, (inactive + free) / 2);
 }