From owner-freebsd-mips@FreeBSD.ORG  Thu Nov 15 18:25:28 2012
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Date: Thu, 15 Nov 2012 12:25:21 -0600
From: Alan Cox <alc@rice.edu>
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Subject: ZERO_REGION_SIZE
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Cc: "Jayachandran C." <jchandra@freebsd.org>
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Given the possibility of L1 cache aliasing on some (many?) MIPS
processors, I think that you, i.e., MIPS users, should evaluate the
performance effects of the following change:

Index: mips/include/vmparam.h
===================================================================
--- mips/include/vmparam.h      (revision 243091)
+++ mips/include/vmparam.h      (working copy)
@@ -190,6 +190,6 @@
  */
 #define        VM_NFREEORDER           9
 
-#define        ZERO_REGION_SIZE        (64 * 1024)     /* 64KB */
+#define        ZERO_REGION_SIZE        4096
 
 #endif /* !_MACHINE_VMPARAM_H_ */

You can quantify the impact with a simple test like:

dd if=/dev/zero of=/dev/null bs=<64 or 128>k count=<something non-trivial>

If possible, please use a kernel without WITNESS or INVARIANTS.

Alan

P.S. I would also be curious how setting this to 8192 would perform.