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From: Konstantin Belousov <kib@FreeBSD.org>
Date: Wed, 29 Aug 2012 15:28:38 +0000 (UTC)
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Subject: svn commit: r239838 - stable/9/sys/kern
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Author: kib
Date: Wed Aug 29 15:28:38 2012
New Revision: 239838
URL: http://svn.freebsd.org/changeset/base/239838

Log:
  MFC r236516:
  Count and export the number of prefaulting happen.

Modified:
  stable/9/sys/kern/vfs_vnops.c
Directory Properties:
  stable/9/sys/   (props changed)

Modified: stable/9/sys/kern/vfs_vnops.c
==============================================================================
--- stable/9/sys/kern/vfs_vnops.c	Wed Aug 29 15:21:27 2012	(r239837)
+++ stable/9/sys/kern/vfs_vnops.c	Wed Aug 29 15:28:38 2012	(r239838)
@@ -56,6 +56,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/filio.h>
 #include <sys/resourcevar.h>
 #include <sys/sx.h>
+#include <sys/sysctl.h>
 #include <sys/ttycom.h>
 #include <sys/conf.h>
 #include <sys/syslog.h>
@@ -766,6 +767,9 @@ unlock:
 }
 
 static const int io_hold_cnt = 16;
+static unsigned long vn_io_faults_cnt;
+SYSCTL_LONG(_debug, OID_AUTO, vn_io_faults, CTLFLAG_RD,
+    &vn_io_faults_cnt, 0, "Count of vn_io_fault lock avoidance triggers");
 
 /*
  * The vn_io_fault() is a wrapper around vn_read() and vn_write() to
@@ -863,6 +867,7 @@ vn_io_fault(struct file *fp, struct uio 
 	if (error != EFAULT)
 		goto out;
 
+	atomic_add_long(&vn_io_faults_cnt, 1);
 	uio_clone->uio_segflg = UIO_NOCOPY;
 	uiomove(NULL, resid - uio->uio_resid, uio_clone);
 	uio_clone->uio_segflg = uio->uio_segflg;