From mboxrd@z Thu Jan 1 00:00:00 1970 Message-Id: <200506271814.j5RIEwg22390@unix-os.sc.intel.com> From: "Chen, Kenneth W" 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 In-Reply-To: <42BFC10E.50204@yahoo.com.au> Sender: owner-linux-mm@kvack.org Return-Path: To: 'Nick Piggin' , Lincoln Dale Cc: Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: 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 -- 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/ . Don't email: aart@kvack.org