linux-kernel - Re: [RFC PATCH v1 0/4] mm, hwpoison: improve handling workload related to hugetlb and memory

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Message-ID: <c424e8a2-a771-e738-396c-24ac907b557f@redhat.com>
Date:   Thu, 12 May 2022 09:28:40 +0200
From:   David Hildenbrand <david@...hat.com>
To:     HORIGUCHI NAOYA(堀口 直也) 
        <naoya.horiguchi@....com>
Cc:     Miaohe Lin <linmiaohe@...wei.com>,
        Oscar Salvador <osalvador@...e.de>,
        Naoya Horiguchi <naoya.horiguchi@...ux.dev>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Yang Shi <shy828301@...il.com>,
        Muchun Song <songmuchun@...edance.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v1 0/4] mm, hwpoison: improve handling workload
 related to hugetlb and memory_hotplug

>>>>
>>>> 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.
> 
> OK, so there seems no need to manipulate struct pages for hwpoison in
> all relevant cases.

Right. When offlining a memory block, all we have to do is remember if
we stumbled over a hwpoisoned page and rememebr that inside the memory
block. Rejecting to online is then easy.

-- 
Thanks,

David / dhildenb