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 CBD6FC433EF for ; Mon, 27 Jun 2022 09:17:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233927AbiF0JR5 (ORCPT ); Mon, 27 Jun 2022 05:17:57 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39838 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233936AbiF0JRz (ORCPT ); Mon, 27 Jun 2022 05:17:55 -0400 Received: from szxga08-in.huawei.com (szxga08-in.huawei.com [45.249.212.255]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 175E662F4; Mon, 27 Jun 2022 02:17:53 -0700 (PDT) Received: from dggpemm500020.china.huawei.com (unknown [172.30.72.56]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4LWhsP34JVz1L8j0; Mon, 27 Jun 2022 17:15:37 +0800 (CST) Received: from dggpemm500006.china.huawei.com (7.185.36.236) by dggpemm500020.china.huawei.com (7.185.36.49) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Mon, 27 Jun 2022 17:17:50 +0800 Received: from [10.174.178.55] (10.174.178.55) by dggpemm500006.china.huawei.com (7.185.36.236) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Mon, 27 Jun 2022 17:17:49 +0800 Subject: Re: [PATCH 5/5] arm64: kdump: Don't defer the reservation of crash high memory To: Baoquan He , Catalin Marinas CC: Kefeng Wang , Ard Biesheuvel , Mark Rutland , Thomas Gleixner , Ingo Molnar , Borislav Petkov , , "H . Peter Anvin" , "Eric Biederman" , Rob Herring , "Frank Rowand" , , Dave Young , Vivek Goyal , , , Will Deacon , , Jonathan Corbet , , Randy Dunlap , Feng Zhou , Chen Zhou , John Donnelly , "Dave Kleikamp" , liushixin References: <20220613080932.663-1-thunder.leizhen@huawei.com> <20220613080932.663-6-thunder.leizhen@huawei.com> <3f66323d-f371-b931-65fb-edfae0f01c88@huawei.com> From: "Leizhen (ThunderTown)" Message-ID: Date: Mon, 27 Jun 2022 17:17:49 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.178.55] X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To dggpemm500006.china.huawei.com (7.185.36.236) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On 2022/6/27 10:52, Baoquan He wrote: > On 06/23/22 at 03:07pm, Catalin Marinas wrote: >> On Wed, Jun 22, 2022 at 04:35:16PM +0800, Baoquan He wrote: >>> On 06/21/22 at 07:04pm, Catalin Marinas wrote: >>>> The problem with splitting is that you can end up with two entries in >>>> the TLB for the same VA->PA mapping (e.g. one for a 4KB page and another >>>> for a 2MB block). In the lucky case, the CPU will trigger a TLB conflict >>>> abort (but can be worse like loss of coherency). >>> >>> Thanks for this explanation. Is this a drawback of arm64 design? X86 >>> code do the same thing w/o issue, is there way to overcome this on >>> arm64 from hardware or software side? >> >> It is a drawback of the arm64 implementations. Having multiple TLB >> entries for the same VA would need additional logic in hardware to >> detect, so the microarchitects have pushed back. In ARMv8.4, some >> balanced was reached with FEAT_BBM so that the only visible side-effect >> is a potential TLB conflict abort that could be resolved by software. > > I see, thx. > >> >>> I ever got a arm64 server with huge memory, w or w/o crashkernel setting >>> have different bootup time. And the more often TLB miss and flush will >>> cause performance cost. It is really a pity if we have very powerful >>> arm64 cpu and system capacity, but bottlenecked by this drawback. >> >> Is it only the boot time affected or the runtime performance as well? > > Sorry for late reply. What I observerd is the boot time serious latecy > with huge memory. Since the timestamp is not available at that time, > we can't tell the number. I didn't notice the runtime performance. There's some data here, and I see you're not on the cc list. https://lore.kernel.org/linux-mm/1656241815-28494-1-git-send-email-guanghuifeng@linux.alibaba.com/T/ > > . > -- Regards, Zhen Lei