From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from verein.lst.de ([213.95.11.211]:33555 "EHLO newverein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726301AbfFYKZm (ORCPT ); Tue, 25 Jun 2019 06:25:42 -0400 Date: Tue, 25 Jun 2019 12:25:07 +0200 From: Christoph Hellwig Subject: Re: [PATCH 07/12] xfs: don't preallocate a transaction for file size updates Message-ID: <20190625102507.GA1986@lst.de> References: <20190624055253.31183-1-hch@lst.de> <20190624055253.31183-8-hch@lst.de> <20190624161720.GQ5387@magnolia> <20190624231523.GC7777@dread.disaster.area> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190624231523.GC7777@dread.disaster.area> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: Dave Chinner Cc: "Darrick J. Wong" , Christoph Hellwig , Damien Le Moal , Andreas Gruenbacher , linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org On Tue, Jun 25, 2019 at 09:15:23AM +1000, Dave Chinner wrote: > > So, uh, how much of a hit do we take for having to allocate a > > transaction for a file size extension? Particularly since we can > > combine those things now? > > Unless we are out of log space, the transaction allocation and free > should be largely uncontended and so it's just a small amount of CPU > usage. i.e it's a slab allocation/free and then lockless space > reservation/free. If we are out of log space, then we sleep waiting > for space - the issue really comes down to where it is better to > sleep in that case.... I see the general point, but we'll still have the same issue with unwritten extent conversion and cow completions, and I don't remember seeing any issue in that regard. And we'd hit exactly that case with random writes to preallocated or COW files, i.e. the typical image file workload.