From owner-svn-src-head@FreeBSD.ORG  Tue Jun 28 06:32:36 2011
Return-Path: <owner-svn-src-head@FreeBSD.ORG>
Delivered-To: svn-src-head@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id 1F2AD106564A;
	Tue, 28 Jun 2011 06:32:36 +0000 (UTC) (envelope-from mm@FreeBSD.org)
Received: from svn.freebsd.org (svn.freebsd.org [IPv6:2001:4f8:fff6::2c])
	by mx1.freebsd.org (Postfix) with ESMTP id 0F0EB8FC13;
	Tue, 28 Jun 2011 06:32:36 +0000 (UTC)
Received: from svn.freebsd.org (localhost [127.0.0.1])
	by svn.freebsd.org (8.14.4/8.14.4) with ESMTP id p5S6WZcn031873;
	Tue, 28 Jun 2011 06:32:35 GMT (envelope-from mm@svn.freebsd.org)
Received: (from mm@localhost)
	by svn.freebsd.org (8.14.4/8.14.4/Submit) id p5S6WZDN031871;
	Tue, 28 Jun 2011 06:32:35 GMT (envelope-from mm@svn.freebsd.org)
Message-Id: <201106280632.p5S6WZDN031871@svn.freebsd.org>
From: Martin Matuska <mm@FreeBSD.org>
Date: Tue, 28 Jun 2011 06:32:35 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
	svn-src-head@freebsd.org
X-SVN-Group: head
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Cc: 
Subject: svn commit: r223622 -
	head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs
X-BeenThere: svn-src-head@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: SVN commit messages for the src tree for head/-current
	<svn-src-head.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/svn-src-head>,
	<mailto:svn-src-head-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/svn-src-head>
List-Post: <mailto:svn-src-head@freebsd.org>
List-Help: <mailto:svn-src-head-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/svn-src-head>,
	<mailto:svn-src-head-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Tue, 28 Jun 2011 06:32:36 -0000

Author: mm
Date: Tue Jun 28 06:32:35 2011
New Revision: 223622
URL: http://svn.freebsd.org/changeset/base/223622

Log:
  Disable vdev cache (readahead) by default.
  
  The vdev cache is very underutilized (hit ratio 30%-70%) and may consume
  excessive memory on systems with many vdevs.
  
  Illumos-gate revision:	13346
  
  Obtained from:	Illumos (Bug #175)
  MFC after:	1 week

Modified:
  head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_cache.c

Modified: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_cache.c
==============================================================================
--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_cache.c	Tue Jun 28 06:26:03 2011	(r223621)
+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_cache.c	Tue Jun 28 06:32:35 2011	(r223622)
@@ -71,9 +71,16 @@
  * 1<<zfs_vdev_cache_bshift byte reads by the vdev_cache (aka software
  * track buffer).  At most zfs_vdev_cache_size bytes will be kept in each
  * vdev's vdev_cache.
+ *
+ * TODO: Note that with the current ZFS code, it turns out that the
+ * vdev cache is not helpful, and in some cases actually harmful.  It
+ * is better if we disable this.  Once some time has passed, we should
+ * actually remove this to simplify the code.  For now we just disable
+ * it by setting the zfs_vdev_cache_size to zero.  Note that Solaris 11
+ * has made these same changes.
  */
 int zfs_vdev_cache_max = 1<<14;			/* 16KB */
-int zfs_vdev_cache_size = 10ULL << 20;		/* 10MB */
+int zfs_vdev_cache_size = 0;
 int zfs_vdev_cache_bshift = 16;
 
 #define	VCBS (1 << zfs_vdev_cache_bshift)	/* 64KB */