[src/trunk]: src/sys/kern If we're only doing a count-only kern.buf sysctl, j...

[simonb <simonb%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/e9d25697bb2c
branches:  trunk
changeset: 1022555:e9d25697bb2c
user:      simonb <simonb%NetBSD.org@localhost>
date:      Sun Jul 25 06:06:40 2021 +0000

description:
If we're only doing a count-only kern.buf sysctl, just return the number
of active members in the pool cache (plus some slop) instead of looking
in all the free buffer list.  Should reduce CPU usage for "systat vm"
to << 1% especially for machines with a larger number of buffers.

diffstat:

 sys/kern/vfs_bio.c |  14 ++++++++++----
 1 files changed, 10 insertions(+), 4 deletions(-)

diffs (42 lines):

diff -r adf80a83036f -r e9d25697bb2c sys/kern/vfs_bio.c
--- a/sys/kern/vfs_bio.c        Sun Jul 25 06:04:40 2021 +0000
+++ b/sys/kern/vfs_bio.c        Sun Jul 25 06:06:40 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: vfs_bio.c,v 1.300 2021/07/24 13:28:14 simonb Exp $     */
+/*     $NetBSD: vfs_bio.c,v 1.301 2021/07/25 06:06:40 simonb Exp $     */
 
 /*-
  * Copyright (c) 2007, 2008, 2009, 2019, 2020 The NetBSD Foundation, Inc.
@@ -123,7 +123,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: vfs_bio.c,v 1.300 2021/07/24 13:28:14 simonb Exp $");
+__KERNEL_RCSID(0, "$NetBSD: vfs_bio.c,v 1.301 2021/07/25 06:06:40 simonb Exp $");
 
 #ifdef _KERNEL_OPT
 #include "opt_bufcache.h"
@@ -1804,6 +1804,14 @@
            elem_size < 1 || elem_count < 0)
                return (EINVAL);
 
+       if (oldp == NULL) {
+               /* count only, don't run through the buffer queues */
+               needed = pool_cache_nget(buf_cache) - pool_cache_nput(buf_cache);
+               *oldlenp = (needed + KERN_BUFSLOP) * elem_size;
+
+               return 0;
+       }
+
        error = 0;
        needed = 0;
        sysctl_unlock();
@@ -1848,8 +1856,6 @@
        sysctl_relock();
 
        *oldlenp = needed;
-       if (oldp == NULL)
-               *oldlenp += KERN_BUFSLOP * elem_size;
 
        return (error);
 }