From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261551AbVF0SQe (ORCPT ); Mon, 27 Jun 2005 14:16:34 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261540AbVF0SQd (ORCPT ); Mon, 27 Jun 2005 14:16:33 -0400 Received: from fmr24.intel.com ([143.183.121.16]:28843 "EHLO scsfmr004.sc.intel.com") by vger.kernel.org with ESMTP id S261533AbVF0SQR (ORCPT ); Mon, 27 Jun 2005 14:16:17 -0400 Message-Id: <200506271814.j5RIEwg22390@unix-os.sc.intel.com> From: "Chen, Kenneth W" To: "'Nick Piggin'" , "Lincoln Dale" Cc: "Andrew Morton" , , Subject: RE: [rfc] lockless pagecache Date: Mon, 27 Jun 2005 11:14:58 -0700 MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit X-Mailer: Microsoft Office Outlook, Build 11.0.6353 Thread-Index: AcV6928keiUVJvUgQleTCfKTXmW9DwASyEyw In-Reply-To: <42BFC10E.50204@yahoo.com.au> X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Nick Piggin wrote on Monday, June 27, 2005 2:04 AM > >> However I think for Oracle and others that use shared memory like > >> this, they are probably not doing linear access, so that would be a > >> net loss. I'm not completely sure (I don't have access to real loads > >> at the moment), but I would have thought those guys would have looked > >> into fault ahead if it were a possibility. > > > > > > i thought those guys used O_DIRECT - in which case, wouldn't the page > > cache not be used? > > > > Well I think they do use O_DIRECT for their IO, but they need to > use the Linux pagecache for their shared memory - that shared > memory being the basis for their page cache. I think. Whatever > the setup I believe they have issues with the tree_lock, which is > why it was changed to an rwlock. Typically shared memory is used as db buffer cache, and O_DIRECT is performed on these buffer cache (hence O_DIRECT on the shared memory). You must be thinking some other workload. Nevertheless, for OLTP type of db workload, tree_lock hasn't been a problem so far. - Ken