Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756756AbXESBWu (ORCPT ); Fri, 18 May 2007 21:22:50 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754645AbXESBWn (ORCPT ); Fri, 18 May 2007 21:22:43 -0400 Received: from cantor.suse.de ([195.135.220.2]:40635 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754305AbXESBWm (ORCPT ); Fri, 18 May 2007 21:22:42 -0400 Date: Sat, 19 May 2007 03:22:35 +0200 From: Nick Piggin To: Hugh Dickins Cc: Linux Kernel Mailing List , Linux Memory Management List , linux-arch@vger.kernel.org Subject: Re: [rfc] increase struct page size?! Message-ID: <20070519012235.GA15569@wotan.suse.de> References: <20070518040854.GA15654@wotan.suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline 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: 1310 Lines: 28 On Fri, May 18, 2007 at 04:42:10PM +0100, Hugh Dickins wrote: > On Fri, 18 May 2007, Nick Piggin wrote: > > > > If we add 8 bytes to struct page on 64-bit machines, it becomes 64 bytes, > > which is quite a nice number for cache purposes. > > > > However we don't have to let those 8 bytes go to waste: we can use them > > to store the virtual address of the page, which kind of makes sense for > > 64-bit, because they can likely to use complicated memory models. > > Sooner rather than later, don't we need those 8 bytes to expand from > atomic_t to atomic64_t _count and _mapcount? Not that we really need > all 64 bits of both, but I don't know how to work atomically with less. Yeah, that would be a very good use of it. > (Why do I have this sneaking feeling that you're actually wanting > to stick something into the lower bits of page->virtual?) No, I just thought I would get even more flamed if I was just adding padding that wasn't even doing _anything_ :) I remembered Ken had a benchmark where page_address was slow, and the rest is history... - 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/