linux-kernel - Re: [PATCH v3 1/4] mm,hwpoison,hugetlb,memory_hotplug: hotremove memory section with hwpoisoned hugepage

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Date:   Sat, 8 Oct 2022 10:33:54 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     HORIGUCHI NAOYA(堀口 直也) 
        <naoya.horiguchi@....com>
CC:     Naoya Horiguchi <naoya.horiguchi@...ux.dev>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Yang Shi <shy828301@...il.com>,
        Oscar Salvador <osalvador@...e.de>,
        Muchun Song <songmuchun@...edance.com>,
        Jane Chu <jane.chu@...cle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/4] mm,hwpoison,hugetlb,memory_hotplug: hotremove
 memory section with hwpoisoned hugepage

On 2022/10/7 8:45, HORIGUCHI NAOYA(堀口 直也) wrote:
> On Wed, Sep 28, 2022 at 05:32:12PM +0800, Miaohe Lin wrote:
>> On 2022/9/28 9:26, Naoya Horiguchi wrote:
>>>>> @@ -1815,6 +1815,13 @@ int __get_huge_page_for_hwpoison(unsigned long pfn, int flags)
> ...
>>>>> @@ -1862,6 +1869,7 @@ static int try_memory_failure_hugetlb(unsigned long pfn, int flags, int *hugetlb
>>>>>  
>>>>>  	if (hwpoison_filter(p)) {
>>>>>  		hugetlb_clear_page_hwpoison(head);
>>>>> +		SetHPageMigratable(head);
>>>>
>>>> Would we set HPageMigratable flag for free hugetlb pages here? IIUC, they're not expected to have this flag set.
>>>
>>> Thank you, you're right.  This should be done in "if (res == 1)" block.
>>
>> If res == 1, it means hugetlb page refcnt is incremented. But it seems this does not necessarily mean
>> HPageMigratable is cleared by __get_huge_page_for_hwpoison() if the hugetlb page is already isolated.
>> If so, we might set HPageMigratable flag back for already isolated hugetlb pages?
> 
> # sorry for my late reply, I was busy with personal matters these days...

That's all right. I was back from my vacation too. Thanks for your work. :)

> 
> Yes, that could happen (and also in the case where MF_COUNT_INCREASED is
> set).  We need store whether HPageMigratable flag is cleared or not in
> __get_huge_page_for_hwpoison().  I'll add a parameter to
> __get_huge_page_for_hwpoison() to return the flag change to the caller.
> But I also think that there're a few internal states during error handling,
> so it might be good to add some structure like "struct hwpoison_control"
> to save such internal states over related functions (not in this series).

That sounds like a good idea.

Thanks,
Miaohe Lin

> 
> Thanks,
> Naoya Horiguchi
>