Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754340AbXIPWvW (ORCPT ); Sun, 16 Sep 2007 18:51:22 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753532AbXIPWvO (ORCPT ); Sun, 16 Sep 2007 18:51:14 -0400 Received: from mx1.Informatik.Uni-Tuebingen.De ([134.2.12.5]:49010 "EHLO mx1.informatik.uni-tuebingen.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753511AbXIPWvM (ORCPT ); Sun, 16 Sep 2007 18:51:12 -0400 From: Goswin von Brederlow To: Linus Torvalds Cc: Joern Engel , Andrea Arcangeli , Goswin von Brederlow , Andrew Morton , Nick Piggin , Christoph Lameter , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Christoph Hellwig , Mel Gorman , William Lee Irwin III , David Chinner , Jens Axboe , Badari Pulavarty , Maxim Levitsky , Fengguang Wu , swin wang , totty.lu@gmail.com, hugh@veritas.com Subject: Re: [00/41] Large Blocksize Support V7 (adds memmap support) In-Reply-To: (Linus Torvalds's message of "Sun, 16 Sep 2007 11:44:09 -0700 (PDT)") References: <20070911060349.993975297@sgi.com> <200709110452.20363.nickpiggin@yahoo.com.au> <20070911121225.GE13132@lazybastard.org> <20070915014449.4f9cdb51.akpm@linux-foundation.org> <87ir6c3z2l.fsf@informatik.uni-tuebingen.de> <20070915155100.GA21861@v2.random> <87tzpvy9cb.fsf@informatik.uni-tuebingen.de> <20070915223032.GA6708@v2.random> <20070916174657.GA2393@lazybastard.org> <20070916182136.GC2393@lazybastard.org> User-Agent: Gnus/5.110006 (No Gnus v0.6) XEmacs/21.4.19 (linux) Date: Mon, 17 Sep 2007 00:51:06 +0200 Message-ID: <87ps0i442t.fsf@informatik.uni-tuebingen.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1766 Lines: 42 Linus Torvalds writes: > On Sun, 16 Sep 2007, J?rn Engel wrote: >> >> My approach is to have one for mount points and ramfs/tmpfs/sysfs/etc. >> which are pinned for their entire lifetime and another for regular >> files/inodes. One could take a three-way approach and have >> always-pinned, often-pinned and rarely-pinned. >> >> We won't get never-pinned that way. > > That sounds pretty good. The problem, of course, is that most of the time, > the actual dentry allocation itself is done before you really know which > case the dentry will be in, and the natural place for actually giving the > dentry lifetime hint is *not* at "d_alloc()", but when we "instantiate" > it with d_add() or d_instantiate(). > > But it turns out that most of the filesystems we care about already use a > special case of "d_add()" that *already* replaces the dentry with another > one in some cases: "d_splice_alias()". > > So I bet that if we just taught "d_splice_alias()" to look at the inode, > and based on the inode just re-allocate the dentry to some other slab > cache, we'd already handle a lot of the cases! > > And yes, you'd end up with the reallocation overhead quite often, but at > least it would now happen only when filling in a dentry, not in the > (*much* more critical) cached lookup path. > > Linus You would only get it for dentries that live long (or your prediction is awfully wrong) and then the reallocation amortizes over time if you will. :) MfG Goswin - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/