From owner-freebsd-fs@FreeBSD.ORG  Mon Oct 28 21:30:07 2013
Return-Path: <owner-freebsd-fs@FreeBSD.ORG>
Delivered-To: freebsd-fs@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org
 [IPv6:2001:1900:2254:206a::19:1])
 (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits))
 (No client certificate requested)
 by hub.freebsd.org (Postfix) with ESMTP id A07D4E08;
 Mon, 28 Oct 2013 21:30:07 +0000 (UTC) (envelope-from slw@zxy.spb.ru)
Received: from zxy.spb.ru (zxy.spb.ru [195.70.199.98])
 by mx1.freebsd.org (Postfix) with ESMTP id 5EBE32FEE;
 Mon, 28 Oct 2013 21:30:07 +0000 (UTC)
Received: from slw by zxy.spb.ru with local (Exim 4.69 (FreeBSD))
 (envelope-from <slw@zxy.spb.ru>)
 id 1VauPs-000PCK-GJ; Tue, 29 Oct 2013 01:32:04 +0400
Date: Tue, 29 Oct 2013 01:32:04 +0400
From: Slawa Olhovchenkov <slw@zxy.spb.ru>
To: Jordan Hubbard <jkh@ixsystems.com>
Subject: Re: ZFS txg implementation flaw
Message-ID: <20131028213204.GX63359@zxy.spb.ru>
References: <20131028092844.GA24997@zxy.spb.ru>
 <9A00B135-7D28-47EB-ADB3-E87C38BAC6B6@ixsystems.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <9A00B135-7D28-47EB-ADB3-E87C38BAC6B6@ixsystems.com>
User-Agent: Mutt/1.5.21 (2010-09-15)
X-SA-Exim-Connect-IP: <locally generated>
X-SA-Exim-Mail-From: slw@zxy.spb.ru
X-SA-Exim-Scanned: No (on zxy.spb.ru); SAEximRunCond expanded to false
Cc: freebsd-fs@freebsd.org, freebsd-current@freebsd.org
X-BeenThere: freebsd-fs@freebsd.org
X-Mailman-Version: 2.1.14
Precedence: list
List-Id: Filesystems <freebsd-fs.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/options/freebsd-fs>,
 <mailto:freebsd-fs-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-fs>
List-Post: <mailto:freebsd-fs@freebsd.org>
List-Help: <mailto:freebsd-fs-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-fs>,
 <mailto:freebsd-fs-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Mon, 28 Oct 2013 21:30:07 -0000

On Mon, Oct 28, 2013 at 02:22:16PM -0700, Jordan Hubbard wrote:

> 
> On Oct 28, 2013, at 2:28 AM, Slawa Olhovchenkov <slw@zxy.spb.ru> wrote:
> 
> > As I see ZFS cretate seperate thread for earch txg writing.
> > Also for writing to L2ARC.
> > As result -- up to several thousands threads created and destoyed per
> > second. And hundreds thousands page allocations, zeroing, maping
> > unmaping and freeing per seconds. Very high overhead.
> 
> How are you measuring the number of threads being created / destroyed?   This claim seems erroneous given how the ZFS thread pool mechanism actually works (and yes, there are thread pools already).
> 
> It would be helpful to both see your measurement methodology and the workload you are using in your tests.

Semi-indirect.
dtrace -n 'fbt:kernel:vm_object_terminate:entry { @traces[stack()] = count(); }'

After some (2-3) seconds 

              kernel`vnode_destroy_vobject+0xb9
              zfs.ko`zfs_freebsd_reclaim+0x2e
              kernel`VOP_RECLAIM_APV+0x78
              kernel`vgonel+0x134
              kernel`vnlru_free+0x362
              kernel`vnlru_proc+0x61e
              kernel`fork_exit+0x11f
              kernel`0xffffffff80cdbfde
             2490

I don't have user process created threads nor do fork/exit.