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=-17.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 9683DC433E0 for ; Wed, 20 Jan 2021 17:52:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5B66B23122 for ; Wed, 20 Jan 2021 17:52:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387672AbhATRvy (ORCPT ); Wed, 20 Jan 2021 12:51:54 -0500 Received: from mail.kernel.org ([198.145.29.99]:41314 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389093AbhATRuT (ORCPT ); Wed, 20 Jan 2021 12:50:19 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 0FEEE22287; Wed, 20 Jan 2021 17:49:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1611164978; bh=gWJ3LYkk8EdHO2U/O11zpJu6VZAjhVPlgiFK9NxvnQc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=NzlzrhGhR64hLDNjdUnWz792iIICFwDeMfctE/Aq4GidHmoQV3zMFzq840JTrIKv9 sYTm0N5YeEIPwszztezGhkeO8kmA4ZWAsaw2oytAoxQD1u1LpM7QHEzGlP/X6fS0jD MwAGVg1fq8mG4WchHTH7wZrosxaDPdMKNIDdfk+5NoxZJ7ChNUUFbTOSFbxFd1LI3U Ukh/4h/GuSH0RK4Ct35Z0ytGFu0YcKeuP14lKpz11V2aDvEZCXypH95+fZ4T9xQrgr fEsiEbi97YuqZvSHp8a0ru87WJPT2oNXKNaAqHP8Kts9q1BLlTETFrx/tjCIvhL1Gd iKgxCND99RFUQ== Date: Wed, 20 Jan 2021 17:49:33 +0000 From: Will Deacon To: Sudarshan Rajagopalan Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, anshuman.khandual@arm.com, david@redhat.com, Mike Rapoport , Mark Rutland , Suren Baghdasaryan Subject: Re: [PATCH 1/1] arm64: reduce section size for sparsemem Message-ID: <20210120174933.GA20981@willie-the-truck> References: <15cf9a2359197fee0168f820c5c904650d07939e.1610146597.git.sudaraja@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <15cf9a2359197fee0168f820c5c904650d07939e.1610146597.git.sudaraja@codeaurora.org> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 08, 2021 at 03:16:00PM -0800, Sudarshan Rajagopalan wrote: > Reducing the section size helps reduce wastage of reserved memory > for huge memory holes in sparsemem model. But having a much smaller > section size bits could break PMD mappings for vmemmap and wouldn't > accomodate the highest order page for certain page size granule configs. > It is determined that SECTION_SIZE_BITS of 27 (128MB) could be ideal > default value for 4K_PAGES that gives least section size without breaking > PMD based vmemmap mappings. For simplicity, 16K_PAGES could follow the > same as 4K_PAGES. And the least SECTION_SIZE_BITS for 64K_PAGES is 29 > that could accomodate MAX_ORDER. > > Signed-off-by: Sudarshan Rajagopalan > Suggested-by: David Hildenbrand > Cc: Will Deacon > Cc: Anshuman Khandual > Cc: Mike Rapoport > Cc: Mark Rutland > Cc: Suren Baghdasaryan > --- > arch/arm64/include/asm/sparsemem.h | 10 ++++++++-- > 1 file changed, 8 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/include/asm/sparsemem.h b/arch/arm64/include/asm/sparsemem.h > index 1f43fcc79738..ff08ff6b677c 100644 > --- a/arch/arm64/include/asm/sparsemem.h > +++ b/arch/arm64/include/asm/sparsemem.h > @@ -7,7 +7,13 @@ > > #ifdef CONFIG_SPARSEMEM > #define MAX_PHYSMEM_BITS CONFIG_ARM64_PA_BITS > -#define SECTION_SIZE_BITS 30 > -#endif > + > +#if defined(CONFIG_ARM64_4K_PAGES) || defined(CONFIG_ARM64_16K_PAGES) > +#define SECTION_SIZE_BITS 27 > +#else > +#define SECTION_SIZE_BITS 29 > +#endif /* CONFIG_ARM64_4K_PAGES || CONFIG_ARM64_16K_PAGES */ > + > +#endif /* CONFIG_SPARSEMEM*/ Please can you repost this in light of the comments from Anshuman? Thanks, Will