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 6D46FC433EF for ; Thu, 2 Jun 2022 09:32:07 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id BAB7A6B0071; Thu, 2 Jun 2022 05:32:06 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id B56976B0072; Thu, 2 Jun 2022 05:32:06 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A1F9A6B0073; Thu, 2 Jun 2022 05:32:06 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 8F1206B0071 for ; Thu, 2 Jun 2022 05:32:06 -0400 (EDT) Received: from smtpin20.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 4705135258 for ; Thu, 2 Jun 2022 09:32:06 +0000 (UTC) X-FDA: 79532779452.20.268E9D5 Received: from mail-pf1-f173.google.com (mail-pf1-f173.google.com [209.85.210.173]) by imf28.hostedemail.com (Postfix) with ESMTP id 559BAC008A for ; Thu, 2 Jun 2022 09:31:23 +0000 (UTC) Received: by mail-pf1-f173.google.com with SMTP id c196so4301407pfb.1 for ; Thu, 02 Jun 2022 02:32:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance-com.20210112.gappssmtp.com; s=20210112; h=message-id:date:mime-version:user-agent:subject:content-language:to :cc:references:from:in-reply-to:content-transfer-encoding; bh=7I3ikvFHTI+6AcR3ilkUpnEXgPD/1szD0jLieUltRxk=; b=ItV3NywPYNHm1FfgUjBMRW09NCS6oZOMYKz9eWsHEfWk8NyiBKqb/2k4YL46y5CYnS blv+H/a7RyNuy6xKLlhF3jjuJhJr5mcHOPtnbO/jkk6avb7yQjCS4MILmz0LsS5C90bQ 2bi6vOnb22JDvS3GDo/U2ag2yMtw9pvUFAWAPHoaf6ogV7rhYjAH7RVXa4ug20vRoC1q 8sbl0XOZqCq4DQ7fsF6gXfURhOy2h7n3cxn2UDORy08kinTTXUX3gSKIz5tIRQXutU96 sjFjTgmRcpZ0ybdSelwgQIopM8JAAX5NjwYRPfgweHy78H1EOXprtzPilNT8DlE6W4nQ Jpzg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:message-id:date:mime-version:user-agent:subject :content-language:to:cc:references:from:in-reply-to :content-transfer-encoding; bh=7I3ikvFHTI+6AcR3ilkUpnEXgPD/1szD0jLieUltRxk=; b=N+mUlm6277ZvC/RoznTExrqe8PaKMPjUdFFWGgz6DZkkqB5NxMo1jjQ1VTJTjGShH9 0iVk+GH79muz2ALYFzTZPzqHfnGyJzshGvaWa1iKNvETPVkzMP+dVHHSeoI0TCQxIoLR J5D5G/cazTPCCahZeHN5gVXOJzgfVZvo4Ajw5UbuRT7zd6ENqXzBwJbpnGPwXQ8lviNO rqs5tzwggn/xMCPPvnlI880DkgI0y/gIWpUrSWQqqct9a0mRRscZFYZNRANia1CXyDIB 3COU3qf7e9wIOdRdBbYexiKKNoRf+Wru1niDoc8RMitfKr8338m5sJFm9e8pHodmkkcU r4Rw== X-Gm-Message-State: AOAM533iinnO/7fcoM07R3PvzRbtu0Lp0auG+lVPj3EZ2MsS2vzK+J3z EtwqZrO5AQjx/wZXpC5c/p7Pyg== X-Google-Smtp-Source: ABdhPJyGhLUAVF5lUAJbWPQRaAlP5yR+8T7MH5RjDJxKjPQKPSggZoMgr0IYcNvpnD6X4KJsg11e7w== X-Received: by 2002:a63:754b:0:b0:3fb:2109:e4d2 with SMTP id f11-20020a63754b000000b003fb2109e4d2mr3421775pgn.447.1654162321444; Thu, 02 Jun 2022 02:32:01 -0700 (PDT) Received: from [10.255.89.136] ([139.177.225.233]) by smtp.gmail.com with ESMTPSA id d15-20020a056a0024cf00b00512ee2f2363sm3131645pfv.99.2022.06.02.02.31.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 02 Jun 2022 02:32:00 -0700 (PDT) Message-ID: Date: Thu, 2 Jun 2022 17:28:00 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.1 Subject: Re: Re: [PATCH 0/3] recover hardware corrupted page by virtio balloon Content-Language: en-US To: David Hildenbrand , Andrew Morton , =?UTF-8?B?SE9SSUdVQ0hJIE5BT1lBKOWggOWPoyDnm7TkuZ8p?= Cc: Peter Xu , Jue Wang , Paolo Bonzini , jasowang@redhat.com, LKML , Linux MM , mst@redhat.com, qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org References: <24a95dea-9ea6-a904-7c0b-197961afa1d1@bytedance.com> <0d266c61-605d-ce0c-4274-b0c7e10f845a@redhat.com> <4b0c3e37-b882-681a-36fc-16cee7e1fff0@bytedance.com> <5f622a65-8348-8825-a167-414f2a8cd2eb@bytedance.com> <484546da-16cc-8070-2a2c-868717b8a75a@redhat.com> From: zhenwei pi In-Reply-To: <484546da-16cc-8070-2a2c-868717b8a75a@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 559BAC008A Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=bytedance-com.20210112.gappssmtp.com header.s=20210112 header.b=ItV3NywP; dmarc=pass (policy=none) header.from=bytedance.com; spf=pass (imf28.hostedemail.com: domain of pizhenwei@bytedance.com designates 209.85.210.173 as permitted sender) smtp.mailfrom=pizhenwei@bytedance.com X-Stat-Signature: wusz7m6dha896wfsthyk4165ob4fksxs X-Rspam-User: X-HE-Tag: 1654162283-807379 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 6/1/22 15:59, David Hildenbrand wrote: > On 01.06.22 04:17, zhenwei pi wrote: >> On 5/31/22 12:08, Jue Wang wrote: >>> On Mon, May 30, 2022 at 8:49 AM Peter Xu wrote: >>>> >>>> On Mon, May 30, 2022 at 07:33:35PM +0800, zhenwei pi wrote: >>>>> A VM uses RAM of 2M huge page. Once a MCE(@HVAy in [HVAx,HVAz)) occurs, the >>>>> 2M([HVAx,HVAz)) of hypervisor becomes unaccessible, but the guest poisons 4K >>>>> (@GPAy in [GPAx, GPAz)) only, it may hit another 511 MCE ([GPAx, GPAz) >>>>> except GPAy). This is the worse case, so I want to add >>>>> '__le32 corrupted_pages' in struct virtio_balloon_config, it is used in the >>>>> next step: reporting 512 * 4K 'corrupted_pages' to the guest, the guest has >>>>> a chance to isolate the other 511 pages ahead of time. And the guest >>>>> actually loses 2M, fixing 512*4K seems to help significantly. >>>> >>>> It sounds hackish to teach a virtio device to assume one page will always >>>> be poisoned in huge page granule. That's only a limitation to host kernel >>>> not virtio itself. >>>> >>>> E.g. there're upstream effort ongoing with enabling doublemap on hugetlbfs >>>> pages so hugetlb pages can be mapped in 4k with it. It provides potential >>>> possibility to do page poisoning with huge pages in 4k too. When that'll >>>> be ready the assumption can go away, and that does sound like a better >>>> approach towards this problem. >>> >>> +1. >>> >>> A hypervisor should always strive to minimize the guest memory loss. >>> >>> The HugeTLB double mapping enlightened memory poisoning behavior (only >>> poison 4K out of a 2MB huge page and 4K in guest) is a much better >>> solution here. To be completely transparent, it's not _strictly_ >>> required to poison the page (whatever the granularity it is) on the >>> host side, as long as the following are true: >>> >>> 1. A hypervisor can emulate the _minimized_ (e.g., 4K) the poison to the guest. >>> 2. The host page with the UC error is "isolated" (could be PG_HWPOISON >>> or in some other way) and prevented from being reused by other >>> processes. >>> >>> For #2, PG_HWPOISON and HugeTLB double mapping enlightened memory >>> poisoning is a good solution. >>> >>>> >>>>> >>>>>> >>>>>> I assume when talking about "the performance memory drops a lot", you >>>>>> imply that this patch set can mitigate that performance drop? >>>>>> >>>>>> But why do you see a performance drop? Because we might lose some >>>>>> possible THP candidates (in the host or the guest) and you want to plug >>>>>> does holes? I assume you'll see a performance drop simply because >>>>>> poisoning memory is expensive, including migrating pages around on CE. >>>>>> >>>>>> If you have some numbers to share, especially before/after this change, >>>>>> that would be great. >>>>>> >>>>> >>>>> The CE storm leads 2 problems I have even seen: >>>>> 1, the memory bandwidth slows down to 10%~20%, and the cycles per >>>>> instruction of CPU increases a lot. >>>>> 2, the THR (/proc/interrupts) interrupts frequently, the CPU has to use a >>>>> lot time to handle IRQ. >>>> >>>> Totally no good knowledge on CMCI, but if 2) is true then I'm wondering >>>> whether it's necessary to handle the interrupts that frequently. When I >>>> was reading the Intel CMCI vector handler I stumbled over this comment: >>>> >>>> /* >>>> * The interrupt handler. This is called on every event. >>>> * Just call the poller directly to log any events. >>>> * This could in theory increase the threshold under high load, >>>> * but doesn't for now. >>>> */ >>>> static void intel_threshold_interrupt(void) >>>> >>>> I think that matches with what I was thinking.. I mean for 2) not sure >>>> whether it can be seen as a CMCI problem and potentially can be optimized >>>> by adjust the cmci threshold dynamically. >>> >>> The CE storm caused performance drop is caused by the extra cycles >>> spent by the ECC steps in memory controller, not in CMCI handling. >>> This is observed in the Google fleet as well. A good solution is to >>> monitor the CE rate closely in user space via /dev/mcelog and migrate >>> all VMs to another host once the CE rate exceeds some threshold. >>> >>> CMCI is a _background_ interrupt that is not handled in the process >>> execution context and its handler is setup to switch to poll (1 / 5 >>> min) mode if there are more than ~ a dozen CEs reported via CMCI per >>> second. >>>> >>>> -- >>>> Peter Xu >>>> >> >> Hi, Andrew, David, Naoya >> >> According to the suggestions, I'd give up the improvement of memory >> failure on huge page in this series. >> >> Is it worth recovering corrupted pages for the guest kernel? I'd follow >> your decision. > > Well, as I said, I am not sure if we really need/want this for a handful > of 4k poisoned pages in a VM. As I suspected, doing so might primarily > be interesting for some sort of de-fragmentation (allow again a higher > order page to be placed at the affected PFNs), not because of the slight > reduction of available memory. A simple VM reboot would get the job > similarly done. > Sure, Let's drop this idea. Thanks to all for the suggestions. Hi, Naoya It seems that memory failure notifier is not required currently, so I'll not push the next version of: [PATCH 1/3] memory-failure: Introduce memory failure notifier [PATCH 2/3] mm/memory-failure.c: support reset PTE during unpoison Thanks you for review work! > As the poisoning refcount code is already a bit shaky as I learned > recently in the context of memory offlining, I do wonder if we really > want to expose the unpoisoning code outside of debugfs (hwpoison) usage. > > Interestingly, unpoison_memory() documents: "This is only done on the > software-level, so it only works for linux injected failures, not real > hardware failures" -- ehm? > I guess unpoison_memory() is designed/tested by hwpoison-inject only, I have no idea to fix memory failure on a hardware platform. I suppose it's the first time that unpoison_memory() is required by hardware-level (balloon VQ). -- zhenwei pi