Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756643AbXIWRtB (ORCPT ); Sun, 23 Sep 2007 13:49:01 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754184AbXIWRsw (ORCPT ); Sun, 23 Sep 2007 13:48:52 -0400 Received: from lazybastard.de ([212.112.238.170]:35801 "EHLO longford.lazybastard.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753644AbXIWRsv (ORCPT ); Sun, 23 Sep 2007 13:48:51 -0400 Date: Sun, 23 Sep 2007 19:44:03 +0200 From: =?utf-8?B?SsO2cm4=?= Engel To: Linus Torvalds Cc: =?utf-8?B?SsO2cm4=?= 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) Message-ID: <20070923174402.GA15525@lazybastard.org> References: <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> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2087 Lines: 48 On Sun, 16 September 2007 11:44:09 -0700, Linus Torvalds wrote: > On Sun, 16 Sep 2007, Jörn 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(). > > [...] > > 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. There may be another approach. We could create a never-pinned cache, without trying hard to keep it full. Instead of moving a hot dentry at dput() time, we move a cold one from the end of lru. And if the lru list is short, we just chicken out. Our definition of "short lru list" can either be based on a ratio of pinned to unpinned dentries or on a metric of cache hits vs. cache misses. I tend to dislike the cache hit metric, because updatedb would cause tons of misses and result in the same mess we have right now. With this double cache, we have a source of slabs to cheaply reap under memory pressure, but still have a performance advantage (memcpy beats disk io by orders of magnitude). Jörn -- The story so far: In the beginning the Universe was created. This has made a lot of people very angry and been widely regarded as a bad move. -- Douglas Adams - 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/