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=-7.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 D00E2C433E0 for ; Tue, 7 Jul 2020 06:47:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B19FD20702 for ; Tue, 7 Jul 2020 06:47:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1594104470; bh=BrZtIR1hwOkOoHdXGn9wxjTp5t53vI5UcpP82sif2/Y=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=zpOcHXJqbgL6q9recC7Jor+0PFQ1VCETllIOVOO0+rKihnkAaTTfyL9Gr6pUCieKr +WXfCK87wsuMXPOq44uqZK9zfxtI/QpMcRB5w/CE8hPTkrbE8R1ONgJpPrWxN63PjO eHc5cbL/d3/VJLqqNtHmdd9Z7CSi7LBqsFO1x/2o= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728237AbgGGGrt (ORCPT ); Tue, 7 Jul 2020 02:47:49 -0400 Received: from mail.kernel.org ([198.145.29.99]:38912 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725825AbgGGGrt (ORCPT ); Tue, 7 Jul 2020 02:47:49 -0400 Received: from kernel.org (unknown [87.71.40.38]) (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 B227C20674; Tue, 7 Jul 2020 06:47:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1594104468; bh=BrZtIR1hwOkOoHdXGn9wxjTp5t53vI5UcpP82sif2/Y=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=n9oqhgML7NeINidunbCuNzMC4nkPUFJTK+zTWLS4wKjrDLNngJj5Zx28lF0Flbc+q ks4LMOClE15odkf0Yuu4L7wEahLWdJszHc0CGFCxSW40KRm8MNlSoXu/ZMbJnqNRAW BMlisLXXtBM6PEjn9TlP8BagxeYgv0XOOTgqP7/4= Date: Tue, 7 Jul 2020 09:47:37 +0300 From: Mike Rapoport To: Hugh Dickins Cc: Andrea Arcangeli , linux-kernel@vger.kernel.org, Alan Cox , Andrew Morton , Andy Lutomirski , Christopher Lameter , Dave Hansen , Idan Yaniv , James Bottomley , "Kirill A. Shutemov" , Matthew Wilcox , Peter Zijlstra , "Reshetova, Elena" , Thomas Gleixner , Tycho Andersen , linux-api@vger.kernel.org, linux-mm@kvack.org, Mike Rapoport Subject: Re: [RFC PATCH v2 1/5] mm: make HPAGE_PxD_{SHIFT,MASK,SIZE} always available Message-ID: <20200707064737.GA9449@kernel.org> References: <20200706172051.19465-1-rppt@kernel.org> <20200706172051.19465-2-rppt@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Hugh, On Mon, Jul 06, 2020 at 10:07:34PM -0700, Hugh Dickins wrote: > On Mon, 6 Jul 2020, Mike Rapoport wrote: > > From: Mike Rapoport > > > > The definitions of shift, mask and size for the second and the third level > > of the leaf pages are available only when CONFIG_TRANSPARENT_HUGEPAGE is > > set. Otherwise they evaluate to BUILD_BUG(). > > > > There is no explanation neither in the code nor in the changelog why the > > usage of, e.g. HPAGE_PMD_SIZE should be only allowed with THP and forbidden > > otherwise while the definitions of HPAGE_PMD_SIZE and HPAGE_PUD_SIZE > > express the sizes better than ambiguous HPAGE_SIZE. > > > > Make HPAGE_PxD_{SHIFT,MASK,SIZE} definitions available unconditionally. > > Adding Andrea to Cc, he's the one who structured it that way, > and should be consulted. > > I'm ambivalent myself. Many's the time I've been irritated by the > BUILD_BUG() in HPAGE_etc, and it's responsible for very many #ifdef > CONFIG_TRANSPARENT_HUGEPAGEs or IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)s > that you find uglily scattered around the source. > > But that's the point of it: it's warning when you write code peculiar > to THP, that is going to bloat the build of kernels without any THP. > > So although I've often been tempted to do as you suggest, I've always > ended up respecting Andrea's intention, and worked around it instead > (sometimes with #ifdef or IS_ENABLED(), sometimes with > PMD_{SHIFT,MASK_SIZE}, sometimes with a local definition). I could do with a local definition as well, but I think HPAGE_PxD_SHIFT is better and more descriptive than ambiguous HPAGE_SHIFT and I was thinking about wider change to use "THP" defines rather than "hugetlb" defines wherever possible. In the end, HPAGE_PMD_SIZE does not have to be associated with THP and limited to it, it just says what is the size of a leaf page at PMD level. > Hugh > > > > > Signed-off-by: Mike Rapoport > > --- > > include/linux/huge_mm.h | 10 ++-------- > > 1 file changed, 2 insertions(+), 8 deletions(-) > > > > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h > > index 71f20776b06c..1f4b44a76e31 100644 > > --- a/include/linux/huge_mm.h > > +++ b/include/linux/huge_mm.h > > @@ -115,7 +115,6 @@ extern struct kobj_attribute shmem_enabled_attr; > > #define HPAGE_PMD_ORDER (HPAGE_PMD_SHIFT-PAGE_SHIFT) > > #define HPAGE_PMD_NR (1< > > > -#ifdef CONFIG_TRANSPARENT_HUGEPAGE > > #define HPAGE_PMD_SHIFT PMD_SHIFT > > #define HPAGE_PMD_SIZE ((1UL) << HPAGE_PMD_SHIFT) > > #define HPAGE_PMD_MASK (~(HPAGE_PMD_SIZE - 1)) > > @@ -124,6 +123,8 @@ extern struct kobj_attribute shmem_enabled_attr; > > #define HPAGE_PUD_SIZE ((1UL) << HPAGE_PUD_SHIFT) > > #define HPAGE_PUD_MASK (~(HPAGE_PUD_SIZE - 1)) > > > > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE > > + > > extern unsigned long transparent_hugepage_flags; > > > > /* > > @@ -316,13 +317,6 @@ static inline struct list_head *page_deferred_list(struct page *page) > > } > > > > #else /* CONFIG_TRANSPARENT_HUGEPAGE */ > > -#define HPAGE_PMD_SHIFT ({ BUILD_BUG(); 0; }) > > -#define HPAGE_PMD_MASK ({ BUILD_BUG(); 0; }) > > -#define HPAGE_PMD_SIZE ({ BUILD_BUG(); 0; }) > > - > > -#define HPAGE_PUD_SHIFT ({ BUILD_BUG(); 0; }) > > -#define HPAGE_PUD_MASK ({ BUILD_BUG(); 0; }) > > -#define HPAGE_PUD_SIZE ({ BUILD_BUG(); 0; }) > > > > static inline int hpage_nr_pages(struct page *page) > > { > > -- > > 2.26.2 -- Sincerely yours, Mike.