From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757113AbXFOCX7 (ORCPT ); Thu, 14 Jun 2007 22:23:59 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752472AbXFOCXw (ORCPT ); Thu, 14 Jun 2007 22:23:52 -0400 Received: from smtp2.linux-foundation.org ([207.189.120.14]:54644 "EHLO smtp2.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751750AbXFOCXv (ORCPT ); Thu, 14 Jun 2007 22:23:51 -0400 Date: Thu, 14 Jun 2007 19:23:40 -0700 From: Andrew Morton To: Christoph Lameter Cc: linux-kernel@vger.kernel.org, hch@infradead.org Subject: Re: [patch 00/14] Page cache cleanup in anticipation of Large Blocksize support Message-Id: <20070614192340.13d99e84.akpm@linux-foundation.org> In-Reply-To: References: <20070614193839.878721298@sgi.com> <20070614130645.cabdff1b.akpm@linux-foundation.org> <20070614143248.736312f8.akpm@linux-foundation.org> <20070614150417.c73fb6b9.akpm@linux-foundation.org> <20070614154939.c94b097f.akpm@linux-foundation.org> <20070614184013.1ff51d34.akpm@linux-foundation.org> X-Mailer: Sylpheed 2.4.1 (GTK+ 2.8.17; x86_64-unknown-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 14 Jun 2007 19:04:27 -0700 (PDT) Christoph Lameter wrote: > > > Of course there is. The seeks are reduced since there are an factor > > > of 16 less metadata blocks. fsck does not read files. It just reads > > > metadata structures. And the larger contiguous areas the faster. > > > > Some metadata is contiguous: inode tables, some directories (if they got > > lucky), bitmap tables. But fsck surely reads them in a single swoop > > anyway, so there's no gain there. > > The metadata needs to refer to 1/16th of the earlier pages that need to be > tracked. metadata is shrunk significantly. Only if the filesystems are altered to use larger blocksizes and if the operator then chooses to use that feature. Then they suck for small-sized (and even medium-sized) files. So you're still talking about corner cases: specialised applications which require careful setup and administrator intervention. What can we do to optimise the common case? > > Other metadata (indirect blocks) are 100% discontiguous, and reading those > > with a 64k IO into 64k of memory is completely dumb. > > The effect of a larger page size is that the filesystem will > place more meta data into a single page instead of spreading it out. > Reading a mass of meta data with a 64k read is an intelligent choice to > make in particular if there is a large series of such reads. Again: requires larger blocksize: specialised, uninteresting for what will remain the common case: 4k blocksize. The alleged fsck benefit is also unrelated to variable PAGE_CACHE_SIZE. It's a feature of larger (unweildy?) blocksize, and xfs already has that working (doesn't it?) There may be some benefits to some future version of ext4.