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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id CD117CCA47C for ; Mon, 4 Jul 2022 14:11:40 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 67FDA6B0072; Mon, 4 Jul 2022 10:11:40 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 609656B0073; Mon, 4 Jul 2022 10:11:40 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4AA0F6B0074; Mon, 4 Jul 2022 10:11:40 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 367F26B0072 for ; Mon, 4 Jul 2022 10:11:40 -0400 (EDT) Received: from smtpin04.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay13.hostedemail.com (Postfix) with ESMTP id 06CA561202 for ; Mon, 4 Jul 2022 14:11:40 +0000 (UTC) X-FDA: 79649605560.04.38286B3 Received: from out30-130.freemail.mail.aliyun.com (out30-130.freemail.mail.aliyun.com [115.124.30.130]) by imf05.hostedemail.com (Postfix) with ESMTP id F00EC100004 for ; Mon, 4 Jul 2022 14:11:37 +0000 (UTC) X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R391e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018046049;MF=guanghuifeng@linux.alibaba.com;NM=1;PH=DS;RN=21;SR=0;TI=SMTPD_---0VINQ1y1_1656943888; Received: from 30.225.28.131(mailfrom:guanghuifeng@linux.alibaba.com fp:SMTPD_---0VINQ1y1_1656943888) by smtp.aliyun-inc.com; Mon, 04 Jul 2022 22:11:29 +0800 Message-ID: <2ae1cae0-ee26-aa59-7ed9-231d67194dce@linux.alibaba.com> Date: Mon, 4 Jul 2022 22:11:27 +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 ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1656943899; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=zntJOVo9o0Y/d5U3LJWZcNEcp4fxHZfKTV7jA7kzPAM=; b=FA2ZBmv4UarS1rk84TGrbFSm7AgRnT9FSkWS92dFMwFzcGDUlnHehuAgWoLq4hlaosm9r5 oaoABauJjIYQsuajztf1PivaDkzfcZUbdinVIvWRpWGaHI6A0Y/8YLDGp/HoxU6JrWjcPV ZFm2fHjJtMwOFR0aZlY/WAgZ7GWvz+Q= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1656943899; a=rsa-sha256; cv=none; b=e1fgUXhhXrDATPdstqznYdwJgNyqDF3+Im4uVnUt53VqUnXYosNepRw7dzQhTPb1BBQqJa TpfiBoL/xboNmloEc5Sta/ZcM2UG3EqC6obmAdO0lxCoHD26OHTJvgkowt9f62Gy6PUzRS I9Spu6O+VZHZVA2YZKPJnIxdVdtt2gU= ARC-Authentication-Results: i=1; imf05.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=alibaba.com; spf=pass (imf05.hostedemail.com: domain of guanghuifeng@linux.alibaba.com designates 115.124.30.130 as permitted sender) smtp.mailfrom=guanghuifeng@linux.alibaba.com X-Stat-Signature: 7s4ded8mukd7pdgnq75i5a7z9grfyhg1 X-Rspamd-Queue-Id: F00EC100004 X-Rspam-User: Authentication-Results: imf05.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=alibaba.com; spf=pass (imf05.hostedemail.com: domain of guanghuifeng@linux.alibaba.com designates 115.124.30.130 as permitted sender) smtp.mailfrom=guanghuifeng@linux.alibaba.com X-Rspamd-Server: rspam06 X-HE-Tag: 1656943897-589294 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: 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 There is another reason. When loading crashkernel finish, the do_kexec_load will use arch_kexec_protect_crashkres to invalid all the pagetable for crashkernel mem(protect crashkernel mem from access). arch_kexec_protect_crashkres--->set_memory_valid--->...--->apply_to_pmd_range In the apply_to_pmd_range, there is a judement： BUG_ON(pud_huge(*pud)). And if the crashkernel use block/section mapping, there will be some error. Namely, it's need to use non block/section mapping for crashkernel mem before shringking. Thanks.