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

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Message-ID: <20221007004501.GA3227576@hori.linux.bs1.fc.nec.co.jp>
Date:   Fri, 7 Oct 2022 00:45:23 +0000
From:   HORIGUCHI NAOYA(堀口　直也) 
        <naoya.horiguchi@....com>
To:     Miaohe Lin <linmiaohe@...wei.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 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...

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).

Thanks,
Naoya Horiguchi