linux-kernel - Re: [PATCH mmotm v1] mm/hwpoison: disable pcp for page_handle

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Message-ID: <20210617111655.GP30378@techsingularity.net>
Date:   Thu, 17 Jun 2021 12:16:55 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     David Hildenbrand <david@...hat.com>
Cc:     Naoya Horiguchi <nao.horiguchi@...il.com>, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...e.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH mmotm v1] mm/hwpoison: disable pcp for
 page_handle_poison()

On Thu, Jun 17, 2021 at 11:28:49AM +0200, David Hildenbrand wrote:
> On 17.06.21 11:26, Naoya Horiguchi wrote:
> > From: Naoya Horiguchi <naoya.horiguchi@....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?
> 

I'd expect MIGRATE_ISOLATE to be sufficient because they should bypass
the PCP list in free_unref_page.

-- 
Mel Gorman
SUSE Labs