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Mon, 4 Jul 2022 13:15:28 +0000 (UTC) X-FDA: 79649463936.11.85E27D3 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by imf11.hostedemail.com (Postfix) with ESMTP id 89DDC400A9 for ; Mon, 4 Jul 2022 13:15:27 +0000 (UTC) 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 979FDB80EEB; Mon, 4 Jul 2022 13:15:25 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 912B2C3411E; Mon, 4 Jul 2022 13:15:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1656940524; bh=W4jY2582373XRTfcKBJP0Y10Z3L0De/BiuG1GjmXPVE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=rO40aR8JqCr9UpcglvqfoRbslQJROtvQhCq6vvefcP3fF4p/PTrmcyYEexIR1qrO1 c6Q21r3H30D8Gg/jJcsP5kAQKNCAIyFoSOzZghoO779bV3N+kYPDB+aHhBIZzd7wnE T5bfOhz2ptu+Af1v9Q0/oOJLkWobYQ2bDUI7zY1MJtFUkT5SePHD/yAS5DlJvZ8A00 LmGC+XEqh/bPyC+lgn6/mKelWvVpJuY5roj1bQHAOkbwpWvS8EJSZZ02B8h8CxDBmc PxoatHneSFnAClVGEl/MxgSZY52FBuVcTSdJdf2FPX24XaEkAwdXfwLb4PgCjgUtgY rCLa/7WXYfKTg== Date: Mon, 4 Jul 2022 14:15:16 +0100 From: Will Deacon To: "guanghui.fgh" 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 Subject: Re: [PATCH v4] arm64: mm: fix linear mem mapping access performance degradation Message-ID: <20220704131516.GC31684@willie-the-truck> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <4accaeda-572f-f72d-5067-2d0999e4d00a@linux.alibaba.com> User-Agent: Mutt/1.10.1 (2018-07-13) ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1656940527; a=rsa-sha256; cv=none; b=P7FOSehDCchbQB0z4h8a+ktt1dr4ZNJsVi05MwBoQpiI4Ory0W5X57c0q51Gv3R7pKUuSN PmCFCkIPqXSolFnAMBPXY4Kb8p71M91CP7mqSdwiQ9H+pEs7i+F8XeRpzyqRCim4Ovpjqw 5NFJOKnYXW2VavP/trbpaK2bEY74ZBU= ARC-Authentication-Results: i=1; imf11.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=rO40aR8J; dmarc=pass (policy=none) header.from=kernel.org; spf=pass (imf11.hostedemail.com: domain of will@kernel.org designates 145.40.68.75 as permitted sender) smtp.mailfrom=will@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1656940527; 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:dkim-signature; bh=YO0fusBNizT95GnnJ0KfZHt9gCkLxsM4UOOujO3+aIY=; b=TKYqRhBLU6vvtJqs72VGEc7/i+2nGop7jE5/x7emmy7wxWslT510rRA/gi/ZinMX2triB2 qsL6ACE1vveb9+5yeqVc0OwK3kOV0wr2opm6oN9/5i0JItp5zTWrWT4kuq2hMBXKkzhGzs nrjmtZEpTBM6+qR2q2R4F9u7SdGVsvU= X-Rspam-User: X-Rspamd-Server: rspam07 Authentication-Results: imf11.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=rO40aR8J; dmarc=pass (policy=none) header.from=kernel.org; spf=pass (imf11.hostedemail.com: domain of will@kernel.org designates 145.40.68.75 as permitted sender) smtp.mailfrom=will@kernel.org X-Stat-Signature: qm3pyhhadi8uq5wij1syctyudryaxzk3 X-Rspamd-Queue-Id: 89DDC400A9 X-HE-Tag: 1656940527-289480 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: 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