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 972FBC433F5 for ; Thu, 12 May 2022 03:04:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244475AbiELDES (ORCPT ); Wed, 11 May 2022 23:04:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34752 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244588AbiELDEN (ORCPT ); Wed, 11 May 2022 23:04:13 -0400 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 363B319FF40 for ; Wed, 11 May 2022 20:04:05 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.57]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4KzGn73SvJzhZ3C; Thu, 12 May 2022 11:03:23 +0800 (CST) Received: from [10.174.177.76] (10.174.177.76) by canpemm500002.china.huawei.com (7.192.104.244) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Thu, 12 May 2022 11:04:02 +0800 Subject: Re: [RFC PATCH v1 0/4] mm, hwpoison: improve handling workload related to hugetlb and memory_hotplug To: David Hildenbrand , =?UTF-8?B?SE9SSUdVQ0hJIE5BT1lBKOWggOWPoyDnm7TkuZ8p?= CC: Oscar Salvador , Naoya Horiguchi , "linux-mm@kvack.org" , Andrew Morton , Mike Kravetz , Yang Shi , Muchun Song , "linux-kernel@vger.kernel.org" References: <20220427042841.678351-1-naoya.horiguchi@linux.dev> <54399815-10fe-9d43-7ada-7ddb55e798cb@redhat.com> <20220427122049.GA3918978@hori.linux.bs1.fc.nec.co.jp> <20220509072902.GB123646@hori.linux.bs1.fc.nec.co.jp> <6a5d31a3-c27f-f6d9-78bb-d6bf69547887@huawei.com> <465902dc-d3bf-7a93-da04-839faddcd699@huawei.com> <0389eac1-af68-56b5-696d-581bb56878b9@redhat.com> <20220511161052.GA224675@hori.linux.bs1.fc.nec.co.jp> <6986a8dd-7211-fb4d-1d66-5b203cad1aab@redhat.com> From: Miaohe Lin Message-ID: Date: Thu, 12 May 2022 11:04:02 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <6986a8dd-7211-fb4d-1d66-5b203cad1aab@redhat.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.177.76] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To canpemm500002.china.huawei.com (7.192.104.244) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/5/12 0:22, David Hildenbrand wrote: > On 11.05.22 18:10, HORIGUCHI NAOYA(堀口 直也) wrote: >> On Wed, May 11, 2022 at 05:11:17PM +0200, David Hildenbrand wrote: >>> On 09.05.22 12:53, Miaohe Lin wrote: >>>> On 2022/5/9 17:58, Oscar Salvador wrote: >>>>> On Mon, May 09, 2022 at 05:04:54PM +0800, Miaohe Lin wrote: >>>>>>>> So that leaves us with either >>>>>>>> >>>>>>>> 1) Fail offlining -> no need to care about reonlining >>>>>> >>>>>> Maybe fail offlining will be a better alternative as we can get rid of many races >>>>>> between memory failure and memory offline? But no strong opinion. :) >>>>> >>>>> If taking care of those races is not an herculean effort, I'd go with >>>>> allowing offlining + disallow re-onlining. >>>>> Mainly because memory RAS stuff. >>>> >>>> This dose make sense to me. Thanks. We can try to solve those races if >>>> offlining + disallow re-onlining is applied. :) >>>> >>>>> >>>>> Now, to the re-onlining thing, we'll have to come up with a way to check >>>>> whether a section contains hwpoisoned pages, so we do not have to go >>>>> and check every single page, as that will be really suboptimal. >>>> >>>> Yes, we need a stable and cheap way to do that. >>> >>> My simplistic approach would be a simple flag/indicator in the memory block devices >>> that indicates that any page in the memory block was hwpoisoned. It's easy to >>> check that during memory onlining and fail it. >>> >>> diff --git a/drivers/base/memory.c b/drivers/base/memory.c >>> index 084d67fd55cc..3d0ef812e901 100644 >>> --- a/drivers/base/memory.c >>> +++ b/drivers/base/memory.c >>> @@ -183,6 +183,9 @@ static int memory_block_online(struct memory_block *mem) >>> struct zone *zone; >>> int ret; >>> >>> + if (mem->hwpoisoned) >>> + return -EHWPOISON; >>> + >>> zone = zone_for_pfn_range(mem->online_type, mem->nid, mem->group, >>> start_pfn, nr_pages); >>> >> >> Thanks for the idea, a simple flag could work if we don't have to consider >> unpoison. If we need consider unpoison, we need remember the last hwpoison >> page in the memory block, so mem->hwpoisoned should be the counter of >> hwpoison pages. > > Right, but unpoisoning+memory offlining+memory onlining is a yet more > extreme use case we don't have to bother about I think. > >> >>> >>> >>> Once the problematic DIMM would actually get unplugged, the memory block devices >>> would get removed as well. So when hotplugging a new DIMM in the same >>> location, we could online that memory again. >> >> What about PG_hwpoison flags? struct pages are also freed and reallocated >> in the actual DIMM replacement? > > Once memory is offline, the memmap is stale and is no longer > trustworthy. It gets reinitialize during memory onlining -- so any > previous PG_hwpoison is overridden at least there. In some setups, we > even poison the whole memmap via page_init_poison() during memory offlining. > I tend to agree with David. The memmap is unreliable after memory is offline. So preventing memory re-online until a new DIMM replacement is a good idea. Thanks! > Apart from that, we should be freeing the memmap in all relevant cases > when removing memory. I remember there are a couple of corner cases, but > we don't really have to care about that. >