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[2003:cb:c701:700:2393:b0f4:ef08:bd51]) by smtp.gmail.com with ESMTPSA id p8-20020a5d48c8000000b0020c5253d907sm2036804wrs.83.2022.05.11.09.22.42 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 11 May 2022 09:22:42 -0700 (PDT) Message-ID: <6986a8dd-7211-fb4d-1d66-5b203cad1aab@redhat.com> Date: Wed, 11 May 2022 18:22:41 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.0 To: =?UTF-8?B?SE9SSUdVQ0hJIE5BT1lBKOWggOWPoyDnm7TkuZ8p?= Cc: Miaohe Lin , 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> From: David Hildenbrand Organization: Red Hat Subject: Re: [RFC PATCH v1 0/4] mm, hwpoison: improve handling workload related to hugetlb and memory_hotplug In-Reply-To: <20220511161052.GA224675@hori.linux.bs1.fc.nec.co.jp> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Stat-Signature: 5ooqzyfyxab8ueudc7pftnak6cjoukgi Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=PHZ6eriD; spf=none (imf07.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 6B3844009E X-HE-Tag: 1652286162-601655 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 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. 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. -- Thanks, David / dhildenb