From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f170.google.com (mail-wi0-f170.google.com [209.85.212.170]) by kanga.kvack.org (Postfix) with ESMTP id E305F6B0253 for ; Tue, 18 Aug 2015 11:43:05 -0400 (EDT) Received: by wibhh20 with SMTP id hh20so112482425wib.0 for ; Tue, 18 Aug 2015 08:43:05 -0700 (PDT) Received: from mail-wi0-f174.google.com (mail-wi0-f174.google.com. [209.85.212.174]) by mx.google.com with ESMTPS id kb8si31025055wjb.134.2015.08.18.08.43.03 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 18 Aug 2015 08:43:04 -0700 (PDT) Received: by wijp15 with SMTP id p15so104114299wij.0 for ; Tue, 18 Aug 2015 08:43:03 -0700 (PDT) Date: Tue, 18 Aug 2015 17:43:00 +0200 From: Michal Hocko Subject: Re: [PATCHv2 3/4] mm: pack compound_dtor and compound_order into one word in struct page Message-ID: <20150818154259.GL5033@dhcp22.suse.cz> References: <1439824145-25397-1-git-send-email-kirill.shutemov@linux.intel.com> <1439824145-25397-4-git-send-email-kirill.shutemov@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1439824145-25397-4-git-send-email-kirill.shutemov@linux.intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: "Kirill A. Shutemov" Cc: Andrew Morton , Hugh Dickins , Andrea Arcangeli , Dave Hansen , Vlastimil Babka , Johannes Weiner , David Rientjes , linux-kernel@vger.kernel.org, linux-mm@kvack.org On Mon 17-08-15 18:09:04, 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. > > Signed-off-by: Kirill A. Shutemov Reviewed-by: Michal Hocko [...] > @@ -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 do we need this ifdef? We can go with short for both 32b and 64b AFAICS. We do not use compound_order for anything else than the order, right? While I am looking at this, it seems we are jugling with type for order quite a lot - int, unsing int and even unsigned long. -- Michal Hocko SUSE Labs -- 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