From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f181.google.com (mail-wi0-f181.google.com [209.85.212.181]) by kanga.kvack.org (Postfix) with ESMTP id 1F9DE6B0253 for ; Fri, 21 Aug 2015 06:52:03 -0400 (EDT) Received: by widdq5 with SMTP id dq5so12847449wid.0 for ; Fri, 21 Aug 2015 03:52:02 -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 s9si14143125wju.150.2015.08.21.03.52.01 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 21 Aug 2015 03:52:01 -0700 (PDT) Received: by wicne3 with SMTP id ne3so12741060wic.0 for ; Fri, 21 Aug 2015 03:52:01 -0700 (PDT) Date: Fri, 21 Aug 2015 12:51:59 +0200 From: Michal Hocko Subject: Re: [PATCHv3 3/5] mm: pack compound_dtor and compound_order into one word in struct page Message-ID: <20150821105159.GA8868@dhcp22.suse.cz> References: <1439976106-137226-1-git-send-email-kirill.shutemov@linux.intel.com> <1439976106-137226-4-git-send-email-kirill.shutemov@linux.intel.com> <20150820162604.1a1dbbfeafefcda4327587af@linux-foundation.org> <20150821071341.GE23723@dhcp22.suse.cz> <20150821104059.GA12016@node.dhcp.inet.fi> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150821104059.GA12016@node.dhcp.inet.fi> Sender: owner-linux-mm@kvack.org List-ID: To: "Kirill A. Shutemov" Cc: Andrew Morton , "Kirill A. Shutemov" , Hugh Dickins , Andrea Arcangeli , Dave Hansen , Vlastimil Babka , Johannes Weiner , David Rientjes , linux-kernel@vger.kernel.org, linux-mm@kvack.org On Fri 21-08-15 13:40:59, Kirill A. Shutemov wrote: > On Fri, Aug 21, 2015 at 09:13:42AM +0200, Michal Hocko wrote: > > On Thu 20-08-15 16:26:04, Andrew Morton wrote: [...] > > > Why not use ushort for 64-bit as well? > > > > Yeah, I have asked the same in the previous round. So I've tried to > > compile with ushort. The resulting code was slightly larger > > text data bss dec hex filename > > 476370 90811 44632 611813 955e5 mm/built-in.o.prev > > 476418 90811 44632 611861 95615 mm/built-in.o.after > > > > E.g. prep_compound_page > > before: > > 4c6b: c7 47 68 01 00 00 00 movl $0x1,0x68(%rdi) > > 4c72: 89 77 6c mov %esi,0x6c(%rdi) > > after: > > 4c6c: 66 c7 47 68 01 00 movw $0x1,0x68(%rdi) > > 4c72: 66 89 77 6a mov %si,0x6a(%rdi) > > > > which looks very similar to me but I am not an expert here so it might > > possible that movw is slower. > > > > __free_pages_ok > > before: > > 63af: 8b 77 6c mov 0x6c(%rdi),%esi > > after: > > 63b1: 0f b7 77 6a movzwl 0x6a(%rdi),%esi > > > > which looks like a worse code to me. Whether this all is measurable or > > worth it I dunno. The ifdef is ugly but maybe the ugliness is a destiny > > for struct page. > > I don't care about the ifdef that much. If you guys prefer to drop it I'm > fine with that. I can live with it. It makes the struct more complicated which is what struck me. If there is a good reason and a better generated code is a good one then I do not object but please make it a separate patch so that we do not wonder why this has been done in the future. -- 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