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

From: Ed Tomlinson (tomlins@cam.org)
Date: Thu Nov 01 2001 - 21:37:11 EST


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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