From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cuda.sgi.com (cuda3.sgi.com [192.48.176.15]) by oss.sgi.com (8.14.3/8.14.3/SuSE Linux 0.8) with ESMTP id o4F1Rv82056168 for ; Fri, 14 May 2010 20:27:59 -0500 Received: from ZenIV.linux.org.uk (localhost [127.0.0.1]) by cuda.sgi.com (Spam Firewall) with ESMTP id 237321B58E39 for ; Fri, 14 May 2010 18:30:11 -0700 (PDT) Received: from ZenIV.linux.org.uk (zeniv.linux.org.uk [195.92.253.2]) by cuda.sgi.com with ESMTP id VWpgZSx1vGeUhHpq for ; Fri, 14 May 2010 18:30:11 -0700 (PDT) Date: Sat, 15 May 2010 02:30:05 +0100 From: Al Viro Subject: Re: [PATCH 0/5] Per-superblock shrinkers Message-ID: <20100515013005.GA31073@ZenIV.linux.org.uk> References: <1273821863-29524-1-git-send-email-david@fromorbit.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <1273821863-29524-1-git-send-email-david@fromorbit.com> List-Id: XFS Filesystem from SGI List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: xfs-bounces@oss.sgi.com Errors-To: xfs-bounces@oss.sgi.com To: Dave Chinner Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, xfs@oss.sgi.com On Fri, May 14, 2010 at 05:24:18PM +1000, Dave Chinner wrote: > > This series reworks the filesystem shrinkers. We currently have a > set of issues with the current filesystem shrinkers: > > 1. There is an dependency between dentry and inode cache > shrinking that is only implicitly defined by the order of > shrinker registration. > 2. The shrinkers need to walk the superblock list and pin > the superblock to avoid unmount races with the sb going > away. > 3. The dentry cache uses per-superblock LRUs and proportions > reclaim between all the superblocks which means we are > doing breadth based reclaim. This means we touch every > superblock for every shrinker call, and may only reclaim > a single dentry at a time from a given superblock. > 4. The inode cache has a global LRU, so it has different > reclaim patterns to the dentry cache, despite the fact > that the dentry cache is generally the only thing that > pins inodes in memory. > 5. Filesystems need to register their own shrinkers for > caches and can't co-ordinate them with the dentry and > inode cache shrinkers. NAK in that form; sb refcounting and iterators had been reworked for .34, so at least it needs rediff on top of that. What's more, it's very obviously broken wrt locking - you are unregistering a shrinker from __put_super(). I.e. grab rwsem exclusively under a spinlock. Essentially, you've turned dropping a _passive_ reference to superblock (currently an operation safe in any context) into an operation allowed only when no fs or vm locks are held by caller. Not going to work... _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754385Ab0EOBaM (ORCPT ); Fri, 14 May 2010 21:30:12 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:48076 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753127Ab0EOBaK (ORCPT ); Fri, 14 May 2010 21:30:10 -0400 Date: Sat, 15 May 2010 02:30:05 +0100 From: Al Viro To: Dave Chinner Cc: linux-kernel@vger.kernel.org, xfs@oss.sgi.com, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 0/5] Per-superblock shrinkers Message-ID: <20100515013005.GA31073@ZenIV.linux.org.uk> References: <1273821863-29524-1-git-send-email-david@fromorbit.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1273821863-29524-1-git-send-email-david@fromorbit.com> User-Agent: Mutt/1.5.20 (2009-08-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, May 14, 2010 at 05:24:18PM +1000, Dave Chinner wrote: > > This series reworks the filesystem shrinkers. We currently have a > set of issues with the current filesystem shrinkers: > > 1. There is an dependency between dentry and inode cache > shrinking that is only implicitly defined by the order of > shrinker registration. > 2. The shrinkers need to walk the superblock list and pin > the superblock to avoid unmount races with the sb going > away. > 3. The dentry cache uses per-superblock LRUs and proportions > reclaim between all the superblocks which means we are > doing breadth based reclaim. This means we touch every > superblock for every shrinker call, and may only reclaim > a single dentry at a time from a given superblock. > 4. The inode cache has a global LRU, so it has different > reclaim patterns to the dentry cache, despite the fact > that the dentry cache is generally the only thing that > pins inodes in memory. > 5. Filesystems need to register their own shrinkers for > caches and can't co-ordinate them with the dentry and > inode cache shrinkers. NAK in that form; sb refcounting and iterators had been reworked for .34, so at least it needs rediff on top of that. What's more, it's very obviously broken wrt locking - you are unregistering a shrinker from __put_super(). I.e. grab rwsem exclusively under a spinlock. Essentially, you've turned dropping a _passive_ reference to superblock (currently an operation safe in any context) into an operation allowed only when no fs or vm locks are held by caller. Not going to work... From mboxrd@z Thu Jan 1 00:00:00 1970 From: Al Viro Subject: Re: [PATCH 0/5] Per-superblock shrinkers Date: Sat, 15 May 2010 02:30:05 +0100 Message-ID: <20100515013005.GA31073@ZenIV.linux.org.uk> References: <1273821863-29524-1-git-send-email-david@fromorbit.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-kernel@vger.kernel.org, xfs@oss.sgi.com, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org To: Dave Chinner Return-path: Content-Disposition: inline In-Reply-To: <1273821863-29524-1-git-send-email-david@fromorbit.com> Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org On Fri, May 14, 2010 at 05:24:18PM +1000, Dave Chinner wrote: > > This series reworks the filesystem shrinkers. We currently have a > set of issues with the current filesystem shrinkers: > > 1. There is an dependency between dentry and inode cache > shrinking that is only implicitly defined by the order of > shrinker registration. > 2. The shrinkers need to walk the superblock list and pin > the superblock to avoid unmount races with the sb going > away. > 3. The dentry cache uses per-superblock LRUs and proportions > reclaim between all the superblocks which means we are > doing breadth based reclaim. This means we touch every > superblock for every shrinker call, and may only reclaim > a single dentry at a time from a given superblock. > 4. The inode cache has a global LRU, so it has different > reclaim patterns to the dentry cache, despite the fact > that the dentry cache is generally the only thing that > pins inodes in memory. > 5. Filesystems need to register their own shrinkers for > caches and can't co-ordinate them with the dentry and > inode cache shrinkers. NAK in that form; sb refcounting and iterators had been reworked for .34, so at least it needs rediff on top of that. What's more, it's very obviously broken wrt locking - you are unregistering a shrinker from __put_super(). I.e. grab rwsem exclusively under a spinlock. Essentially, you've turned dropping a _passive_ reference to superblock (currently an operation safe in any context) into an operation allowed only when no fs or vm locks are held by caller. Not going to work... -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org