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From: Konstantin Belousov <kib@FreeBSD.org>
Date: Sun, 3 Jun 2012 16:06:56 +0000 (UTC)
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Subject: svn commit: r236516 - head/sys/kern
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Author: kib
Date: Sun Jun  3 16:06:56 2012
New Revision: 236516
URL: http://svn.freebsd.org/changeset/base/236516

Log:
  Count and export the number of prefaulting happen.
  
  MFC after:	 1 month

Modified:
  head/sys/kern/vfs_vnops.c

Modified: head/sys/kern/vfs_vnops.c
==============================================================================
--- head/sys/kern/vfs_vnops.c	Sun Jun  3 14:54:50 2012	(r236515)
+++ head/sys/kern/vfs_vnops.c	Sun Jun  3 16:06:56 2012	(r236516)
@@ -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>
@@ -696,6 +697,9 @@ 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
@@ -793,6 +797,7 @@ 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;