Re: new OOM heuristic failure (was: Re: VM: qsbench)

[Stephan von Krawczynski <skraw@ithnet.com>]

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Hello Lorenzo,

please find attached next vmscan.c patch which sums up the delayed swap_out
(first patch), the fix for not swapping when nr_pages is reached, and (new) the
idea to swap more pages in one call to swap_out if priority gets higher.

I have not the slightest idea what all this does to the performance. Especially
the "more" swap_out code is a pure try-and-error type of thing. Can you do some
testing please?

Thanks,
Stephan

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--- linux-orig/mm/vmscan.c	Thu Nov  1 15:33:58 2001
+++ linux/mm/vmscan.c	Fri Nov  2 13:50:31 2001
@@ -290,7 +290,7 @@
 static int FASTCALL(swap_out(unsigned int priority, unsigned int gfp_mask, zone_t * classzone));
 static int swap_out(unsigned int priority, unsigned int gfp_mask, zone_t * classzone)
 {
-	int counter, nr_pages = SWAP_CLUSTER_MAX;
+	int counter, nr_pages = SWAP_CLUSTER_MAX * DEF_PRIORITY / priority;
 	struct mm_struct *mm;
 
 	counter = mmlist_nr;
@@ -334,7 +334,7 @@
 {
 	struct list_head * entry;
 	int max_scan = nr_inactive_pages / priority;
-	int max_mapped = nr_pages*10;
+	int max_mapped = SWAP_CLUSTER_MAX * DEF_PRIORITY / priority;
 
 	spin_lock(&pagemap_lru_lock);
 	while (--max_scan >= 0 && (entry = inactive_list.prev) != &inactive_list) {
@@ -469,16 +469,10 @@
 			spin_unlock(&pagecache_lock);
 			UnlockPage(page);
 page_mapped:
-			if (--max_mapped >= 0)
-				continue;
+			if (max_mapped > 0)
+				max_mapped--;
+			continue;
 
-			/*
-			 * Alert! We've found too many mapped pages on the
-			 * inactive list, so we start swapping out now!
-			 */
-			spin_unlock(&pagemap_lru_lock);
-			swap_out(priority, gfp_mask, classzone);
-			return nr_pages;
 		}
 
 		/*
@@ -514,6 +508,14 @@
 		break;
 	}
 	spin_unlock(&pagemap_lru_lock);
+
+	/*
+	 * Alert! We've found too many mapped pages on the
+	 * inactive list, so we start swapping out - delayed!
+	 * -skraw
+	 */
+	if (max_mapped==0 && nr_pages>0)
+		swap_out(priority, gfp_mask, classzone);
 
 	return nr_pages;
 }