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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 13F97C433EF for ; Tue, 5 Jul 2022 13:35:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232214AbiGENfK (ORCPT ); Tue, 5 Jul 2022 09:35:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50616 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231324AbiGENew (ORCPT ); Tue, 5 Jul 2022 09:34:52 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 527901EAEC for ; Tue, 5 Jul 2022 05:56:39 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id C5778B817DD for ; Tue, 5 Jul 2022 12:56:35 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id F2418C341C7; Tue, 5 Jul 2022 12:56:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1657025794; bh=/DkYeQmQMOp7ocOqXErwSAITKoW0dXUGUzjZIpwaCAQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=VlSYE0suFgc8JYonqgLLHklZJIU8r838nt4yo7iiToxsUJW9tT05b1sd9ghCytjjJ 7QLZwcvp62iwxGzt6rYEL4o0jDGavZGwpXXKuo8y9GlnCasZA0NNyU6Ft1T+9ajkXY Ewqz/3GZQxsDhk8AyDzmuncJEIHOHKofOScSSsS1T/MVkrDR439ofwFqJRxf8KML3F 3F9LsZC77qu69MhnVru5m+QVNe7whdhpiNVGHSN1IcdNA1TUQQpiN6+RfClV9X1Bt+ 1x2uzsIQXUIAuPKSM08LIhGMf/XkdCMn5jlxEphmTyeqiQjWkvX8/TZ/YqbG8wkFI+ V/KMvE1nVJ79g== Date: Tue, 5 Jul 2022 15:56:14 +0300 From: Mike Rapoport To: Will Deacon Cc: "guanghui.fgh" , Ard Biesheuvel , baolin.wang@linux.alibaba.com, catalin.marinas@arm.com, akpm@linux-foundation.org, david@redhat.com, jianyong.wu@arm.com, james.morse@arm.com, quic_qiancai@quicinc.com, christophe.leroy@csgroup.eu, jonathan@marek.ca, mark.rutland@arm.com, thunder.leizhen@huawei.com, anshuman.khandual@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, geert+renesas@glider.be, linux-mm@kvack.org, yaohongbo@linux.alibaba.com, alikernel-developer@linux.alibaba.com Subject: Re: [PATCH v4] arm64: mm: fix linear mem mapping access performance degradation Message-ID: References: <4accaeda-572f-f72d-5067-2d0999e4d00a@linux.alibaba.com> <20220704131516.GC31684@willie-the-truck> <2ae1cae0-ee26-aa59-7ed9-231d67194dce@linux.alibaba.com> <20220704142313.GE31684@willie-the-truck> <6977c692-78ca-5a67-773e-0389c85f2650@linux.alibaba.com> <20220704163815.GA32177@willie-the-truck> <20220705095231.GB552@willie-the-truck> <5d044fdd-a61a-d60f-d294-89e17de37712@linux.alibaba.com> <20220705121115.GB1012@willie-the-truck> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220705121115.GB1012@willie-the-truck> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 05, 2022 at 01:11:16PM +0100, Will Deacon wrote: > On Tue, Jul 05, 2022 at 08:07:07PM +0800, guanghui.fgh wrote: > > > > 1.The rodata full is harm to the performance and has been disabled in-house. > > > > 2.When using crashkernel with rodata non full, the kernel also will use non > > block/section mapping which cause high d-TLB miss and degrade performance > > greatly. > > This patch fix it to use block/section mapping as far as possible. > > > > bool can_set_direct_map(void) > > { > > return rodata_full || debug_pagealloc_enabled(); > > } > > > > map_mem: > > if (can_set_direct_map() || IS_ENABLED(CONFIG_KFENCE)) > > flags |= NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS; > > > > 3.When rodata full is disabled, crashkernel also need protect(keep > > arch_kexec_[un]protect_crashkres using). > > I think crashkernel should't depend on radata full(Maybe other architecture > > don't support radata full now). > > I think this is going round in circles :/ > > As a first step, can we please leave the crashkernel mapped unless > rodata=full? It should be a much simpler patch to write, review and maintain > and it gives you the performance you want when crashkernel is being used. Since we are talking about large systems, what do you think about letting them set CRASH_ALIGN to PUD_SIZE, then unmap(crashkernel); __create_pgd_mapping(crashkernel, NO_BLOCK_MAPPINGS); should be enough to make crash kernel mapped with base pages. > Will -- Sincerely yours, Mike.