From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from aserp2120.oracle.com ([141.146.126.78]:36978 "EHLO aserp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726586AbeLCQfR (ORCPT ); Mon, 3 Dec 2018 11:35:17 -0500 Date: Mon, 3 Dec 2018 08:34:57 -0800 From: "Darrick J. Wong" Subject: Re: [PATCH] fs/xfs: Add support for passing write life-time hint with log Message-ID: <20181203163457.GW8125@magnolia> References: <1543842769-6363-1-git-send-email-joshi.k@samsung.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: Holger =?iso-8859-1?Q?Hoffst=E4tte?= Cc: Kanchan Joshi , linux-xfs@vger.kernel.org On Mon, Dec 03, 2018 at 04:48:12PM +0100, Holger Hoffstätte wrote: > On 12/3/18 2:12 PM, Kanchan Joshi wrote: > > Log gets updated in a circular fashion, and that makes life-time > > of log-data different from other types of meta/user-data. > > By passing a write life-time hint with log, GC efficiency of multi-stream SSD > > gets improved, leading to endurance/performance benefits. > > It is described in greater detail (along with results) in this "FAST 2018" > > paper - > > https://www.usenix.org/conference/fast18/presentation/rho > > This patch introduces new mount option "logwritehint" to pass write hint > > with XFS log. > > Is there any downside to passing the hints unconditionally? Why wouldn't we always pass LIFE_EXTREME? Do people have setups where, say, hint <= LIFE_MEDIUM gets a disk but anything longer than that gets a big slow stone tablet, which is not where we'd want the metadata log? For that matter, should we be passing write hints for other fs metadata? Fixed AG headers never move, should they be LIFE_whateverthelogis ? How about space and file metadata, which aren't fixed to certain locations? > Introducing a new mount option which depends on the internals of > an SSD seems .. unlikely to gain many friends. > Otherwise a great idea. :) Likewise, I'm not wild about adding mount options or passing raw integers via mount(8) command line: mount /dev/fd0 /mnt -o logwritehint=3 # ??? --D > -h