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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 19F74C10F27 for ; Wed, 11 Mar 2020 13:13:12 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id B23C622464 for ; Wed, 11 Mar 2020 13:13:11 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="eAs0JVwh" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B23C622464 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 1C4B76B0003; Wed, 11 Mar 2020 09:13:11 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 177B36B0006; Wed, 11 Mar 2020 09:13:11 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 08D4F6B0007; Wed, 11 Mar 2020 09:13:11 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0125.hostedemail.com [216.40.44.125]) by kanga.kvack.org (Postfix) with ESMTP id E84EF6B0003 for ; Wed, 11 Mar 2020 09:13:10 -0400 (EDT) Received: from smtpin20.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id B46438248047 for ; Wed, 11 Mar 2020 13:13:10 +0000 (UTC) X-FDA: 76583122140.20.power08_38cc20b3b0233 X-HE-Tag: power08_38cc20b3b0233 X-Filterd-Recvd-Size: 3126 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) by imf17.hostedemail.com (Postfix) with ESMTP for ; Wed, 11 Mar 2020 13:13:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=sziWq6MWN5OyTxoksdD/WPMN/xCI8OkAv9KSBboIXI0=; b=eAs0JVwhIDOAloqqtt45eXddKN Unz/qCWwauodMbAPvgI3K6U64+lMfXCYQQO2Zwb4V+3d7dJJ+SZi267gnbwhbORW2bk5xzbIur5pp zkVHwD8oYbhu35RNXGe5a+1b4oaycDF2XAwYLcjw0xLgV5gBb4D+VByTjVl7UcNQcffZNIbwoNYEn 2+u2fnTP43mutLRvYWR0mO6TIPJIrAHAU8doQRXGTa3uR7WMmhsb7euvOylOc0fsGD8Mt9C9MTESi c7CpoVQ9TmaWw+ufzguM8nzE40ipjiJdUehnHq/zgWK34wlzfUjR1DQiYWvB8RihI1oD+Vtx0izuM lh/GUl4w==; Received: from willy by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1jC1AX-0006q5-1T; Wed, 11 Mar 2020 13:13:05 +0000 Date: Wed, 11 Mar 2020 06:13:04 -0700 From: Matthew Wilcox To: Alexander Duyck Cc: Andrew Morton , Vlastimil Babka , linux-mm Subject: Re: [PATCH] mm: Make PageType more efficient Message-ID: <20200311131304.GD22433@bombadil.infradead.org> References: <20200310185609.5401-1-willy@infradead.org> <20200310203732.GC22433@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 easier for humans to read and reason about. Do you have an opinion which one you'd like to see?