[PATCH] alloc_pages priority tuning

Fix up the logic which decides when the caller can dip into page reserves.

- If the caller has realtime scheduling policy, or if the caller cannot run
  direct reclaim, then allow the caller to use up to a quarter of the page
  reserves.

- If the caller has __GFP_HIGH then allow the caller to use up to half of
  the page reserves.

- If the caller has PF_MEMALLOC then the caller can use 100% of the page
  reserves.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

mm/page_alloc.c

@@ -607,9 +607,17 @@ __alloc_pages(unsigned int gfp_mask, unsigned int order,
 	int i;
 	int alloc_type;
 	int do_retry;
+	int can_try_harder;
 
 	might_sleep_if(wait);
 
+	/*
+	 * The caller may dip into page reserves a bit more if the caller
+	 * cannot run direct reclaim, or is the caller has realtime scheduling
+	 * policy
+	 */
+	can_try_harder = (unlikely(rt_task(p)) && !in_interrupt()) || !wait;
+
 	zones = zonelist->zones;  /* the list of zones suitable for gfp_mask */
 
 	if (unlikely(zones[0] == NULL)) {
@@ -641,9 +649,9 @@ __alloc_pages(unsigned int gfp_mask, unsigned int order,
 	for (i = 0; (z = zones[i]) != NULL; i++) {
 		min = z->pages_min;
 		if (gfp_mask & __GFP_HIGH)
-			min -= min>>1;
-		if (unlikely(rt_task(p)) && !in_interrupt())
-			min -= min>>2;
+			min /= 2;
+		if (can_try_harder)
+			min -= min / 4;
 		min += (1<<order) + z->protection[alloc_type];
 
 		if (z->free_pages < min)
@@ -684,9 +692,9 @@ __alloc_pages(unsigned int gfp_mask, unsigned int order,
 	for (i = 0; (z = zones[i]) != NULL; i++) {
 		min = z->pages_min;
 		if (gfp_mask & __GFP_HIGH)
-			min -= min>>1;
-		if (unlikely(rt_task(p)) && !in_interrupt())
-			min -= min>>2;
+			min /= 2;
+		if (can_try_harder)
+			min -= min / 4;
 		min += (1<<order) + z->protection[alloc_type];
 
 		if (z->free_pages < min)