Allow maxusers to scale on machines with large address space.

Some hooks are added to clamp down maxusers and nmbclusters for
small address space systems.

VM_MAX_AUTOTUNE_MAXUSERS - the max maxusers that will be autotuned based on
physical memory.
VM_MAX_AUTOTUNE_NMBCLUSTERS - max nmbclusters based on physical memory.

These are set to the old values on i386 to preserve the clamping that was
being done to all arches.

Another macro VM_AUTOTUNE_NMBCLUSTERS is provided to allow an override
for the calculation on a MD basis.  Currently no arch defines this.

Reviewed by: peter
MFC after: 2 weeks

1 files changed, 11 insertions, 11 deletions

diff --git a/sys/kern/subr_param.c b/sys/kern/subr_param.c
index 5c9af32..b953e78 100644
--- a/sys/kern/subr_param.c
+++ b/sys/kern/subr_param.c
@@ -278,17 +278,17 @@ init_param2(long physpages)
 		maxusers = physpages / (2 * 1024 * 1024 / PAGE_SIZE);
 		if (maxusers < 32)
 			maxusers = 32;
-		/*
-		 * Clips maxusers to 384 on machines with <= 4GB RAM or 32bit.
-		 * Scales it down 6x for large memory machines.
-		 */
-		if (maxusers > 384) {
-			if (sizeof(void *) <= 4)
-			    maxusers = 384;
-			else
-			    maxusers = 384 + ((maxusers - 384) / 6);
-		}
-	}
+#ifdef VM_MAX_AUTOTUNE_MAXUSERS
+                if (maxusers > VM_MAX_AUTOTUNE_MAXUSERS)
+                        maxusers = VM_MAX_AUTOTUNE_MAXUSERS;
+#endif
+                /*
+                 * Scales down the function in which maxusers grows once
+                 * we hit 384.
+                 */
+                if (maxusers > 384)
+                        maxusers = 384 + ((maxusers - 384) / 8);
+        }
 
 	/*
 	 * The following can be overridden after boot via sysctl.  Note: