From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f43.google.com (mail-pa0-f43.google.com [209.85.220.43]) by kanga.kvack.org (Postfix) with ESMTP id 9AB066B0253 for ; Thu, 20 Aug 2015 19:26:07 -0400 (EDT) Received: by pawq9 with SMTP id q9so38116021paw.3 for ; Thu, 20 Aug 2015 16:26:07 -0700 (PDT) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id da3si9760869pdb.56.2015.08.20.16.26.06 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 20 Aug 2015 16:26:06 -0700 (PDT) Date: Thu, 20 Aug 2015 16:26:04 -0700 From: Andrew Morton 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> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: 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 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, 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: email@kvack.org