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=-0.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,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 060D6C10DCE for ; Wed, 11 Mar 2020 01:10:31 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 879AC21927 for ; Wed, 11 Mar 2020 01:10:30 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="kD7ZGFSa" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 879AC21927 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 039EF6B0003; Tue, 10 Mar 2020 21:10:30 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id F06386B0006; Tue, 10 Mar 2020 21:10:29 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DF44A6B0007; Tue, 10 Mar 2020 21:10:29 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0226.hostedemail.com [216.40.44.226]) by kanga.kvack.org (Postfix) with ESMTP id C26916B0003 for ; Tue, 10 Mar 2020 21:10:29 -0400 (EDT) Received: from smtpin05.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 7ABBF180AD81D for ; Wed, 11 Mar 2020 01:10:29 +0000 (UTC) X-FDA: 76581300978.05.rest31_43fd18a81e45 X-HE-Tag: rest31_43fd18a81e45 X-Filterd-Recvd-Size: 3103 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf41.hostedemail.com (Postfix) with ESMTP for ; Wed, 11 Mar 2020 01:10:29 +0000 (UTC) Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 0A17B21927; Wed, 11 Mar 2020 01:10:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1583889028; bh=WHHp8SmAuPCABkN27rOy/Xnf/FlKnEYHSNbD2a/uSD4=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=kD7ZGFSaXP/1CjERN+4rdQfXpPAUgXIb8tu6z2UwQKwqI6cIrJZjAKI01Es1/bjGJ 9Nzt+IDIHNoDlPGbwysHDQhhBq5ubePTTnMm+dxEmn3glxMeiM2nQ+IUUXHU9IOG3V NPjn5zrwmt1g2zPtLYzmF7x2s+56K1mZ7FrUoY/s= Date: Tue, 10 Mar 2020 18:10:27 -0700 From: Andrew Morton To: Matthew Wilcox Cc: Vlastimil Babka , linux-mm@kvack.org, Alexander Duyck Subject: Re: [PATCH] mm: Make PageType more efficient Message-Id: <20200310181027.232cff5b00600e1f056a4177@linux-foundation.org> In-Reply-To: <20200310185609.5401-1-willy@infradead.org> References: <20200310185609.5401-1-willy@infradead.org> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit 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 Tue, 10 Mar 2020 11:56:09 -0700 Matthew Wilcox wrote: > From: "Matthew Wilcox (Oracle)" > > PageType is a little hard for GCC to reason about, By checking > ((~A) & flag) instead of (flag & (A | MASK) == MASK), GCC can do > better optimisations, saving 652 bytes in page_alloc.o (which is > a heavy user of PageBuddy). > > ... > > --- a/include/linux/page-flags.h > +++ b/include/linux/page-flags.h > @@ -725,14 +725,14 @@ PAGEFLAG_FALSE(DoubleMap) > #define PG_table 0x00000400 > #define PG_guard 0x00000800 > > -#define PageType(page, flag) \ > - ((page->page_type & (PAGE_TYPE_BASE | flag)) == PAGE_TYPE_BASE) > - > static inline int page_has_type(struct page *page) > { > return (int)page->page_type < PAGE_MAPCOUNT_RESERVE; > } > > +#define PageType(page, flag) \ > + (page_has_type(page) && (~page->page_type & flag)) > + `flag' should be parenthesized here. As should `page' if one is even more paranoid. I tried this: --- a/include/linux/page-flags.h~mm-make-pagetype-more-efficient-fix +++ a/include/linux/page-flags.h @@ -731,7 +731,7 @@ static inline int page_has_type(struct p } #define PageType(page, flag) \ - (page_has_type(page) && (~page->page_type & flag)) + (page_has_type(page) && !(page->page_type & ~(flag))) #define PAGE_TYPE_OPS(uname, lname) \ static __always_inline int Page##uname(struct page *page) \ and page_alloc.o shrunk by 6782 bytes, half of it in get_page_from_freelist(). Something crazy is going on. gcc-7.2.0.