From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E107AC0044D for ; Wed, 11 Mar 2020 17:14:49 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 44F3F2072F for ; Wed, 11 Mar 2020 17:14:50 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 44F3F2072F Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 334146B0003; Wed, 11 Mar 2020 13:14:49 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 312166B0005; Wed, 11 Mar 2020 13:14:49 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 221116B0006; Wed, 11 Mar 2020 13:14:49 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0005.hostedemail.com [216.40.44.5]) by kanga.kvack.org (Postfix) with ESMTP id 0BB396B0003 for ; Wed, 11 Mar 2020 13:14:49 -0400 (EDT) Received: from smtpin11.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id B61488245571 for ; Wed, 11 Mar 2020 17:14:48 +0000 (UTC) X-FDA: 76583731056.11.shake73_813ddafffee58 X-HE-Tag: shake73_813ddafffee58 X-Filterd-Recvd-Size: 3097 Received: from mga12.intel.com (mga12.intel.com [192.55.52.136]) by imf46.hostedemail.com (Postfix) with ESMTP for ; Wed, 11 Mar 2020 17:14:47 +0000 (UTC) X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga106.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 11 Mar 2020 10:14:46 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,541,1574150400"; d="scan'208";a="236519480" Received: from iweiny-desk2.sc.intel.com ([10.3.52.147]) by orsmga008.jf.intel.com with ESMTP; 11 Mar 2020 10:14:45 -0700 Date: Wed, 11 Mar 2020 10:14:45 -0700 From: Ira Weiny To: Matthew Wilcox Cc: Alexander Duyck , Andrew Morton , Vlastimil Babka , linux-mm Subject: Re: [PATCH] mm: Make PageType more efficient Message-ID: <20200311171444.GA1446196@iweiny-DESK2.sc.intel.com> References: <20200310185609.5401-1-willy@infradead.org> <20200310203732.GC22433@bombadil.infradead.org> <20200311131304.GD22433@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200311131304.GD22433@bombadil.infradead.org> User-Agent: Mutt/1.11.1 (2018-12-01) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Mar 11, 2020 at 06:13:04AM -0700, Matthew Wilcox wrote: > On Tue, Mar 10, 2020 at 02:50:50PM -0700, Alexander Duyck wrote: > > On Tue, Mar 10, 2020 at 1:37 PM Matthew Wilcox wrote: > > > > > -#define PageType(page, flag) \ > > > > > - ((page->page_type & (PAGE_TYPE_BASE | flag)) == PAGE_TYPE_BASE) > > > > > - > > > > >From what I can tell this is the only consumer of PAGE_TYPE_BASE. > > Since it is removed you can probably remove that definition as well. > > I _could_ ... I do want to indicate to people that they probably > shouldn't use those bits in order to leave space for overflow and > wraparound of _mapcount. > > > > > > +#define PageType(page, flag) \ > > > > > + (page_has_type(page) && (~page->page_type & flag)) > > > > You can probably spare a cycle or two here by testing for > > "!(page->page_type & flag)". That way you avoid the extra bit flipping > > since the compiler can just handle the result of the AND op as it sees > > fit. > > GCC already knows to do that optimisation; mm/page_alloc.o is identical > (same md5sum) when changing from (~page->page_type & flag) to > !(page->page_type & flag). So it's just a question of which one is No dog in this fight... But for simpletons like me... !(page->page_type & flag) ... makes much more sense, Ira > easier for humans to read and reason about. Do you have an opinion > which one you'd like to see? > >