From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 14 Sep 2005 07:59:32 +1000 From: David Chinner Subject: Re: VM balancing issues on 2.6.13: dentry cache not getting shrunk enough Message-ID: <20050913215932.GA1654338@melbourne.sgi.com> References: <20050911105709.GA16369@thunk.org> <20050911120045.GA4477@in.ibm.com> <20050912031636.GB16758@thunk.org> <20050913084752.GC4474@in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20050913084752.GC4474@in.ibm.com> Sender: owner-linux-mm@kvack.org Return-Path: To: Bharata B Rao Cc: Theodore Ts'o , Dipankar Sarma , linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: On Tue, Sep 13, 2005 at 02:17:52PM +0530, Bharata B Rao wrote: > > Second is Sonny Rao's rbtree dentry reclaim patch which is an attempt > to improve this dcache fragmentation problem. FYI, in the past I've tried this patch to reduce dcache fragmentation on an Altix (16k pages, 62 dentries to a slab page) under heavy fileserver workloads and it had no measurable effect. It appeared that there was almost always at least one active dentry on each page in the slab. The story may very well be different on 4k page machines, however. Typically, fragmentation was bad enough that reclaim removed ~90% of the working set of dentries to free about 1% of the memory in the dentry slab. We had to get down to freeing > 95% of the dentry cache before fragmentation started to reduce and the system stopped trying to reclaim the dcache which we then spent the next 10 minutes repopulating...... We also tried separating out directory dentries into a separate slab so that (potentially) longer lived dentries were clustered together rather than sparsely distributed around the slab cache. Once again, it had no measurable effect on the level of fragmentation (with or without the rbtree patch). FWIW, the inode cache was showing very similar levels of fragmentation under reclaim as well. Cheers, Dave. -- Dave Chinner R&D Software Enginner SGI Australian Software Group -- 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