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 5C48FC433EF for ; Mon, 4 Jul 2022 13:41:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232727AbiGDNlR (ORCPT ); Mon, 4 Jul 2022 09:41:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49248 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229448AbiGDNlP (ORCPT ); Mon, 4 Jul 2022 09:41:15 -0400 Received: from out30-45.freemail.mail.aliyun.com (out30-45.freemail.mail.aliyun.com [115.124.30.45]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E843B10A5 for ; Mon, 4 Jul 2022 06:41:13 -0700 (PDT) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R701e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018046050;MF=guanghuifeng@linux.alibaba.com;NM=1;PH=DS;RN=21;SR=0;TI=SMTPD_---0VINPxtk_1656942066; Received: from 30.225.28.131(mailfrom:guanghuifeng@linux.alibaba.com fp:SMTPD_---0VINPxtk_1656942066) by smtp.aliyun-inc.com; Mon, 04 Jul 2022 21:41:08 +0800 Message-ID: <3e6f5c5d-3503-8625-be6e-132daa0390f3@linux.alibaba.com> Date: Mon, 4 Jul 2022 21:41:05 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH v4] arm64: mm: fix linear mem mapping access performance degradation To: Will Deacon Cc: 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, rppt@kernel.org, geert+renesas@glider.be, ardb@kernel.org, linux-mm@kvack.org, yaohongbo@linux.alibaba.com, alikernel-developer@linux.alibaba.com References: <1656777473-73887-1-git-send-email-guanghuifeng@linux.alibaba.com> <20220704103523.GC31437@willie-the-truck> <73f0c53b-fd17-c5e9-3773-1d71e564eb50@linux.alibaba.com> <20220704111402.GA31553@willie-the-truck> <4accaeda-572f-f72d-5067-2d0999e4d00a@linux.alibaba.com> <20220704131516.GC31684@willie-the-truck> From: "guanghui.fgh" In-Reply-To: <20220704131516.GC31684@willie-the-truck> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Thanks. 在 2022/7/4 21:15, Will Deacon 写道: > On Mon, Jul 04, 2022 at 08:05:59PM +0800, guanghui.fgh wrote: >> >> >> 在 2022/7/4 19:14, Will Deacon 写道: >>> On Mon, Jul 04, 2022 at 06:58:20PM +0800, guanghui.fgh wrote: >>>> >>>> >>>> 在 2022/7/4 18:35, Will Deacon 写道: >>>>> On Sat, Jul 02, 2022 at 11:57:53PM +0800, Guanghui Feng wrote: >>>>>> The arm64 can build 2M/1G block/sectiion mapping. When using DMA/DMA32 zone >>>>>> (enable crashkernel, disable rodata full, disable kfence), the mem_map will >>>>>> use non block/section mapping(for crashkernel requires to shrink the region >>>>>> in page granularity). But it will degrade performance when doing larging >>>>>> continuous mem access in kernel(memcpy/memmove, etc). >>>>> >>>>> Hmm. It seems a bit silly to me that we take special care to unmap the >>>>> crashkernel from the linear map even when can_set_direct_map() is false, as >>>>> we won't be protecting the main kernel at all! >>>>> >>>>> Why don't we just leave the crashkernel mapped if !can_set_direct_map() >>>>> and then this problem just goes away? >>>> >>>> This question had been asked lask week. >>> >>> Sorry, I didn't spot that. Please could you link me to the conversation, as >>> I'm still unable to find it in my inbox? >> >> Please access this link: >> https://lore.kernel.org/linux-arm-kernel/075b0a8e-cb7e-70f6-b45a-54cd31886794@linux.alibaba.com/T/ > > Sorry, but I read through the thread and I still can't find where the > possibility of leaving the crashkernel mapped was discussed > >>>> 1.Quoted messages from arch/arm64/mm/init.c >>>> >>>> "Memory reservation for crash kernel either done early or deferred >>>> depending on DMA memory zones configs (ZONE_DMA) -- >>>> >>>> In absence of ZONE_DMA configs arm64_dma_phys_limit initialized >>>> here instead of max_zone_phys(). This lets early reservation of >>>> crash kernel memory which has a dependency on arm64_dma_phys_limit. >>>> Reserving memory early for crash kernel allows linear creation of block >>>> mappings (greater than page-granularity) for all the memory bank rangs. >>>> In this scheme a comparatively quicker boot is observed. >>>> >>>> If ZONE_DMA configs are defined, crash kernel memory reservation >>>> is delayed until DMA zone memory range size initialization performed in >>>> zone_sizes_init(). The defer is necessary to steer clear of DMA zone >>>> memory range to avoid overlap allocation. >>>> >>>> [[[ >>>> So crash kernel memory boundaries are not known when mapping all bank memory >>>> ranges, which otherwise means not possible to exclude crash kernel range >>>> from creating block mappings so page-granularity mappings are created for >>>> the entire memory range. >>>> ]]]" >>>> >>>> Namely, the init order: memblock init--->linear mem mapping(4k mapping for >>>> crashkernel, requirinig page-granularity changing))--->zone dma >>>> limit--->reserve crashkernel. >>>> So when enable ZONE DMA and using crashkernel, the mem mapping using 4k >>>> mapping. >>> >>> Yes, I understand that is how things work today but I'm saying that we may >>> as well leave the crashkernel mapped (at block granularity) if >>> !can_set_direct_map() and then I think your patch becomes a lot simpler. >> >> But Page-granularity mapppings are necessary for crash kernel memory range >> for shrinking its size via /sys/kernel/kexec_crash_size interfac(Quoted from >> arch/arm64/mm/init.c). >> So this patch split block/section mapping to 4k page-granularity mapping for >> crashkernel mem. > > Why? I don't see why the mapping granularity is relevant at all if we > always leave the whole thing mapped. > > Will I have find the commit 06a7f711246b081afc21fff859f1003f1f2a0fbc adding /sys/kernel/kexec_crash_size for changing crashkernel mem size. "Implement shrinking the reserved memory for crash kernel, if it is more than enough." Maybe we could use block/section mapping for crashkernle mem, and split a part of crashkernel mem block/section mapping when shringking(by writing to /sys/kernel/kexec_crash_size(handled by crash_shrink_memory, crash_free_reserved_phys_range)). (Maybe there is no need to split all crashkernle mem block/section mapping at boot time). Thanks.