From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: with ECARTIS (v1.0.0; list xfs); Fri, 31 Aug 2007 07:34:01 -0700 (PDT) Received: from pentafluge.infradead.org (pentafluge.infradead.org [213.146.154.40]) by oss.sgi.com (8.12.10/8.12.10/SuSE Linux 0.7) with ESMTP id l7VEXt4p030095 for ; Fri, 31 Aug 2007 07:33:57 -0700 Subject: Re: [PATCH] Increase lockdep MAX_LOCK_DEPTH From: Peter Zijlstra In-Reply-To: <20070831135042.GD422459@sgi.com> References: <46D79C62.1010304@sandeen.net> <1188542389.6112.44.camel@twins> <20070831135042.GD422459@sgi.com> Content-Type: text/plain Date: Fri, 31 Aug 2007 16:33:51 +0200 Message-Id: <1188570831.6112.64.camel@twins> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: xfs-bounce@oss.sgi.com Errors-to: xfs-bounce@oss.sgi.com List-Id: xfs To: David Chinner Cc: Eric Sandeen , linux-kernel Mailing List , xfs-oss , Ingo Molnar On Fri, 2007-08-31 at 23:50 +1000, David Chinner wrote: > On Fri, Aug 31, 2007 at 08:39:49AM +0200, Peter Zijlstra wrote: > > On Thu, 2007-08-30 at 23:43 -0500, Eric Sandeen wrote: > > > The xfs filesystem can exceed the current lockdep > > > MAX_LOCK_DEPTH, because when deleting an entire cluster of inodes, > > > they all get locked in xfs_ifree_cluster(). The normal cluster > > > size is 8192 bytes, and with the default (and minimum) inode size > > > of 256 bytes, that's up to 32 inodes that get locked. Throw in a > > > few other locks along the way, and 40 seems enough to get me through > > > all the tests in the xfsqa suite on 4k blocks. (block sizes > > > above 8K will still exceed this though, I think) > > > > As 40 will still not be enough for people with larger block sizes, this > > does not seems like a solid solution. Could XFS possibly batch in > > smaller (fixed sized) chunks, or does that have significant down sides? > > The problem is not filesystem block size, it's the xfs inode cluster buffer > size / the size of the inodes that determines the lock depth. the common case > is 8k/256 = 32 inodes in a buffer, and they all get looked during inode > cluster writeback. > > This inode writeback clustering is one of the reasons XFS doesn't suffer from > atime issues as much as other filesystems - it doesn't need to do as much I/O > to write back dirty inodes to disk. > > IOWs, we are not going to make the inode clusters smallers - if anything they > are going to get *larger* in future so we do less I/O during inode writeback > than we do now..... Since they are all trylocks it seems to suggest there is no hard _need_ to lock a whole inode cluster at once, and could iterate through it with less inodes locked. Granted I have absolutely no understanding of what I'm talking about :-) Trouble is, we'd like to have a sane upper bound on the amount of held locks at any one time, obviously this is just wanting, because a lot of lock chains also depend on the number of online cpus...