From owner-freebsd-fs@FreeBSD.ORG  Thu Mar 19 15:52:24 2015
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 TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits))
 (No client certificate requested)
 by hub.freebsd.org (Postfix) with ESMTPS id CD300F33;
 Thu, 19 Mar 2015 15:52:24 +0000 (UTC)
Received: from phk.freebsd.dk (phk.freebsd.dk [130.225.244.222])
 by mx1.freebsd.org (Postfix) with ESMTP id 8FD035E3;
 Thu, 19 Mar 2015 15:52:24 +0000 (UTC)
Received: from critter.freebsd.dk (unknown [192.168.48.2])
 by phk.freebsd.dk (Postfix) with ESMTP id 9AFFA3BB86;
 Thu, 19 Mar 2015 15:47:08 +0000 (UTC)
Received: from critter.freebsd.dk (localhost [127.0.0.1])
 by critter.freebsd.dk (8.14.9/8.14.9) with ESMTP id t2JFl8Pp078211;
 Thu, 19 Mar 2015 15:47:08 GMT (envelope-from phk@phk.freebsd.dk)
To: Alexander Motin <mav@FreeBSD.org>
Subject: Re: MMCSD erase optimization not quite right?
In-reply-to: <550AA479.2020404@FreeBSD.org>
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
References: <54E80BB6.2040501@glup.org> <54F42B6B.9080307@FreeBSD.org>
 <550A15E6.4060903@glup.org> <550AA479.2020404@FreeBSD.org>
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <78209.1426780028.1@critter.freebsd.dk>
Date: Thu, 19 Mar 2015 15:47:08 +0000
Message-ID: <78210.1426780028@critter.freebsd.dk>
Cc: freebsd-fs@FreeBSD.org, john hood <cgull@glup.org>
X-BeenThere: freebsd-fs@freebsd.org
X-Mailman-Version: 2.1.18-1
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: Thu, 19 Mar 2015 15:52:24 -0000

--------
In message <550AA479.2020404@FreeBSD.org>, Alexander Motin writes:

>> Also, UFS perhaps
>> shouldn't issue BIO_DELETE immediately, because the block might be
>> reused soon (I'm not sure what the right answer here is for best flash
>> performance).

If you reuse a block quickly, the BIO_DELETE is "wasted" in the sense
that the new write would do the same job, but unless you know something
about your reuse pattern that allows you to optimize this aspect,
statistically the best strategy is to BIO_DELETE as soon as possible.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.