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Subject: Re: [PATCH mmotm v1] mm/hwpoison: disable pcp for
 page_handle_poison()
To:     Naoya Horiguchi <nao.horiguchi@gmail.com>, linux-mm@kvack.org
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Mel Gorman <mgorman@techsingularity.net>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Oscar Salvador <osalvador@suse.de>,
        Michal Hocko <mhocko@suse.com>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>,
        linux-kernel@vger.kernel.org
References: <20210617092626.291006-1-nao.horiguchi@gmail.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
Message-ID: <e7f75111-5b65-8756-2764-f5c98c4747ea@redhat.com>
Date:   Thu, 17 Jun 2021 11:28:49 +0200
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On 17.06.21 11:26, Naoya Horiguchi wrote:
> From: Naoya Horiguchi <naoya.horiguchi@nec.com>
> 
> Recent changes by patch "mm/page_alloc: allow high-order pages to be
> stored on the per-cpu lists" makes kernels determine whether to use pcp
> by pcp_allowed_order(), which breaks soft-offline for hugetlb pages.
> 
> Soft-offline dissolves a migration source page, then removes it from
> buddy free list, so it's assumed that any subpage of the soft-offlined
> hugepage are recognized as a buddy page just after returning from
> dissolve_free_huge_page().  pcp_allowed_order() returns true for
> hugetlb, so this assumption is no longer true.
> 
> So disable pcp during dissolve_free_huge_page() and
> take_page_off_buddy() to prevent soft-offlined hugepages from linking to
> pcp lists.  Soft-offline should not be common events so the impact on
> performance should be minimal.  And I think that the optimization of
> Mel's patch could benefit to hugetlb so zone_pcp_disable() is called
> only in hwpoison context.

Mel, Oscar, does alloc_contig_range() now have similar issues or is it 
avoided because the pageblock(s) are set MIGRATE_ISOLATE?


-- 
Thanks,

David / dhildenb