Module Name: src
Committed By: joerg
Date: Mon Sep 8 22:01:24 UTC 2014
Modified Files:
src/sys/kern: vfs_bio.c
Log Message:
Replace random with cprng_fast32. Reorganise computation to replace
(32bit) division with (long) multiplication.
To generate a diff of this commit:
cvs rdiff -u -r1.251 -r1.252 src/sys/kern/vfs_bio.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/kern/vfs_bio.c
diff -u src/sys/kern/vfs_bio.c:1.251 src/sys/kern/vfs_bio.c:1.252
--- src/sys/kern/vfs_bio.c:1.251 Fri Sep 5 05:57:21 2014
+++ src/sys/kern/vfs_bio.c Mon Sep 8 22:01:24 2014
@@ -1,4 +1,4 @@
-/* $NetBSD: vfs_bio.c,v 1.251 2014/09/05 05:57:21 matt Exp $ */
+/* $NetBSD: vfs_bio.c,v 1.252 2014/09/08 22:01:24 joerg Exp $ */
/*-
* Copyright (c) 2007, 2008, 2009 The NetBSD Foundation, Inc.
@@ -123,7 +123,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: vfs_bio.c,v 1.251 2014/09/05 05:57:21 matt Exp $");
+__KERNEL_RCSID(0, "$NetBSD: vfs_bio.c,v 1.252 2014/09/08 22:01:24 joerg Exp $");
#include "opt_bufcache.h"
@@ -143,6 +143,7 @@ __KERNEL_RCSID(0, "$NetBSD: vfs_bio.c,v
#include <sys/cpu.h>
#include <sys/wapbl.h>
#include <sys/bitops.h>
+#include <sys/cprng.h>
#include <uvm/uvm.h> /* extern struct uvm uvm */
@@ -532,7 +533,7 @@ bufinit2(void)
static int
buf_lotsfree(void)
{
- int guess, thresh;
+ u_long guess;
/* Always allocate if less than the low water mark. */
if (bufmem < bufmem_lowater)
@@ -548,16 +549,14 @@ buf_lotsfree(void)
/*
* The probabily of getting a new allocation is inversely
- * proportional to the current size of the cache, using
- * a granularity of 16 steps.
+ * proportional to the current size of the cache above
+ * the low water mark. Divide the total first to avoid overflows
+ * in the product.
*/
- guess = random() & 0x0000000fL;
+ guess = cprng_fast32() % 16;
- /* Don't use "16 * bufmem" here to avoid a 32-bit overflow. */
- thresh = (bufmem - bufmem_lowater) /
- ((bufmem_hiwater - bufmem_lowater) / 16);
-
- if (guess >= thresh)
+ if ((bufmem_hiwater - bufmem_lowater) / 16 * guess >=
+ (bufmem - bufmem_lowater))
return 1;
/* Otherwise don't allocate. */
