From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 24 Jun 2002 14:34:31 -0700 From: "Martin J. Bligh" Subject: Re: [PATCH] (1/2) reverse mapping VM for 2.5.23 (rmap-13b) Message-ID: <6660000.1024954471@flay> In-Reply-To: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline Sender: owner-linux-mm@kvack.org Return-Path: To: Linus Torvalds , Craig Kulesa Cc: Ingo Molnar , Rik van Riel , Dave Jones , Daniel Phillips , linux-kernel@vger.kernel.org, linux-mm@kvack.org, rwhron@earthlink.net List-ID: >> I'll try a more varied set of tests tonight, with cpu usage tabulated. > > Please do a few non-swap tests too. > > Swapping is the thing that rmap is supposed to _help_, so improvements in > that area are good (and had better happen!), but if you're only looking at > the swap performance, you're ignoring the known problems with rmap, ie the > cases where non-rmap kernels do really well. > > Comparing one but not the other doesn't give a very balanced picture.. It would also be interesting to see memory consumption figures for a benchmark with many large processes. With this type of load, memory consumption through PTEs is already a problem - as far as I can see, rmap triples the memory requirement of PTEs through the PTE chain's doubly linked list (an additional 8 bytes per entry) ... perhaps my calculations are wrong? This is particular problem for databases that tend to have thousands of processes attatched to a large shared memory area. A quick rough calculation indicates that the Oracle test I was helping out with was consuming almost 10Gb of PTEs without rmap - 30Gb for overhead doesn't sound like fun to me ;-( M. -- 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/