Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030222AbWL3Cp6 (ORCPT ); Fri, 29 Dec 2006 21:45:58 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1030223AbWL3Cp6 (ORCPT ); Fri, 29 Dec 2006 21:45:58 -0500 Received: from mx1.redhat.com ([66.187.233.31]:56512 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030222AbWL3Cp5 (ORCPT ); Fri, 29 Dec 2006 21:45:57 -0500 Date: Fri, 29 Dec 2006 21:45:54 -0500 From: Dave Jones To: Linux Kernel Subject: potential for buffer_head shrinkage. Message-ID: <20061230024554.GA12306@redhat.com> Mail-Followup-To: Dave Jones , Linux Kernel Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.4.2.2i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 751 Lines: 21 Looking at struct buffer_head, it seems that b_state uses at most 15 bits, where it's defined as a 64bit entity due to it being used by bit_spin_lock and friends. Given it's not uncommon for a few hundred thousand of these to be present, I wonder if it's worth the effort of folding b_count into the upper bits of b_state, thus shrinking buffer_head by 16 bits? This would still leave 32 bits 'wasted' for further bh_state_bits expansion if necessary. Opinions? Dave -- http://www.codemonkey.org.uk - 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/