[uPATCH] Nulling mmap_cache iff needed (2.4.0)

[Rasmus Andersen]

Hi.

The following (trivial) patch against 2.4.0 (but should apply cleanly
against 241p1) makes do_munmap only null our precious cache if the
pointer contained therein is invalidated by the unmapping. I doubt it
will make any measurable difference but it seems straightforward
enough to be done anyway.

Running kernel compiles and starting X/gnome with this patch raises my 
cache hit rate a couple of percentage points, and I have a feeling that
there might be work loads out there that hit this kernel path more often
that these.

Comments?

diff -aur linux-2.4.0-clean/mm/mmap.c linux/mm/mmap.c
--- linux-2.4.0-clean/mm/mmap.c	Sat Dec 30 18:35:19 2000
+++ linux/mm/mmap.c	Tue Jan  9 23:30:03 2001
@@ -712,7 +712,10 @@
 		if (mm->mmap_avl)
 			avl_remove(mpnt, &mm->mmap_avl);
 	}
-	mm->mmap_cache = NULL;	/* Kill the cache. */
+	if (mm->mmap_cache && mm->mmap_cache->vm_start < addr+len 
+	    && mm->mmap_cache->vm_end > addr)
+		mm->mmap_cache = NULL;	/* Kill the cache. */
+
 	spin_unlock(&mm->page_table_lock);
 
 	/* Ok - we have the memory areas we should free on the 'free' list,

-- 
Regards,
        Rasmus([e-mail])

"It's like an Alcatraz around my neck."
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