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From: Ed Tomlinson <tomlins@cam.org>
Organization: me
To: linux-kernel@vger.kernel.org
Subject: Re: new OOM heuristic failure  (was: Re: VM: qsbench)
Date: Thu, 1 Nov 2001 21:37:11 -0500
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Hi,

shrink_caches can end up lying.  shrink_dcache_memory and friends do not tell 
shrink_caches how many pages they free so nr_pages can be bogus...  Is it worth 
fixing?  The simpliest, harmlessly racey and not too pretty, code follows.  It 
would also not be hard to change the shrink_ calls to return the number of pages 
shrunk, but this would hit more code...

Comments?

Ed Tomlinson

--- linux/mm/vmscan.c.orig	Wed Oct 31 14:11:33 2001
+++ linux/mm/vmscan.c	Wed Oct 31 14:51:58 2001
@@ -552,6 +552,7 @@
 static int shrink_caches(zone_t * classzone, int priority, unsigned int gfp_mask, int nr_pages)
 {
 	int chunk_size = nr_pages;
+	int nr_shrunk;
 	unsigned long ratio;
 
 	nr_pages -= kmem_cache_reap(gfp_mask);
@@ -567,11 +568,21 @@
 	if (nr_pages <= 0)
 		return 0;
 
+	nr_shrunk = nr_free_pages;
+
 	shrink_dcache_memory(priority, gfp_mask);
 	shrink_icache_memory(priority, gfp_mask);
 #ifdef CONFIG_QUOTA
 	shrink_dqcache_memory(DEF_PRIORITY, gfp_mask);
 #endif
+
+	/* racey - calculate how many pages we got from shrinks */
+	nr_shrunk = nr_free_pages - nr_shrunk; 
+	if (nr_shrunk > 0) {
+		nr_pages -= nr_shrunk;
+		if (nr_pages <= 0)
+			return 0;
+	}
 
 	return nr_pages;
 }
-
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