[patch 07/19] (NEW) add some sanity checks to get_scan_ratio

[Rik van Riel <riel@redhat.com>]

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The access ratio based scan rate determination in get_scan_ratio
works ok in most situations, but needs to be corrected in some
corner cases:
- if we run out of swap space, do not bother scanning the anon LRUs
- if we have already freed all of the page cache, we need to scan
  the anon LRUs

Signed-off-by: Rik van Riel <riel@redhat.com>

Index: linux-2.6.24-rc6-mm1/mm/vmscan.c
===================================================================
--- linux-2.6.24-rc6-mm1.orig/mm/vmscan.c	2008-01-07 17:33:50.000000000 -0500
+++ linux-2.6.24-rc6-mm1/mm/vmscan.c	2008-01-07 17:57:49.000000000 -0500
@@ -1182,7 +1182,7 @@ static unsigned long shrink_list(enum lr
 static void get_scan_ratio(struct zone *zone, struct scan_control * sc,
 					unsigned long *percent)
 {
-	unsigned long anon, file;
+	unsigned long anon, file, free;
 	unsigned long anon_prio, file_prio;
 	unsigned long rotate_sum;
 	unsigned long ap, fp;
@@ -1230,6 +1230,20 @@ static void get_scan_ratio(struct zone *
 	else if (fp > 100)
 		fp = 100;
 	percent[1] = fp;
+
+	free = zone_page_state(zone, NR_FREE_PAGES);
+
+	/*
+	 * If we have no swap space, do not bother scanning anon pages
+	 */
+	if (nr_swap_pages <= 0)
+		percent[0] = 0;
+	/*
+	 * If we already freed most file pages, scan the anon pages
+	 * regardless of the page access ratios or swappiness setting.
+	 */
+	else if (file + free <= zone->pages_high)
+		percent[0] = 100;
 }
 
 

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