Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753259AbbHTX0I (ORCPT ); Thu, 20 Aug 2015 19:26:08 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:58757 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752580AbbHTX0G (ORCPT ); Thu, 20 Aug 2015 19:26:06 -0400 Date: Thu, 20 Aug 2015 16:26:04 -0700 From: Andrew Morton To: "Kirill A. Shutemov" Cc: Hugh Dickins , Andrea Arcangeli , Dave Hansen , Vlastimil Babka , Johannes Weiner , Michal Hocko , David Rientjes , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCHv3 3/5] mm: pack compound_dtor and compound_order into one word in struct page Message-Id: <20150820162604.1a1dbbfeafefcda4327587af@linux-foundation.org> In-Reply-To: <1439976106-137226-4-git-send-email-kirill.shutemov@linux.intel.com> References: <1439976106-137226-1-git-send-email-kirill.shutemov@linux.intel.com> <1439976106-137226-4-git-send-email-kirill.shutemov@linux.intel.com> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1418 Lines: 41 On Wed, 19 Aug 2015 12:21:44 +0300 "Kirill A. Shutemov" wrote: > The patch halves space occupied by compound_dtor and compound_order in > struct page. > > For compound_order, it's trivial long -> int/short conversion. > > For get_compound_page_dtor(), we now use hardcoded table for destructor > lookup and store its index in the struct page instead of direct pointer > to destructor. It shouldn't be a big trouble to maintain the table: we > have only two destructor and NULL currently. > > This patch free up one word in tail pages for reuse. This is preparation > for the next patch. > > ... > > @@ -145,8 +143,13 @@ struct page { > */ > /* First tail page of compound page */ > struct { > - compound_page_dtor *compound_dtor; > - unsigned long compound_order; > +#ifdef CONFIG_64BIT > + unsigned int compound_dtor; > + unsigned int compound_order; > +#else > + unsigned short int compound_dtor; > + unsigned short int compound_order; > +#endif Why not use ushort for 64-bit as well? It would be clearer if that new enum had a name, so we use "enum compound_dtor_id" everywhere instead of a bare uint. -- 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/