Re: [PATCH mmotm v1] mm/hwpoison: disable pcp for page_handle_poison()

[Mel Gorman <mgorman@techsingularity.net>]

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@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?
> 

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

-- 
Mel Gorman
SUSE Labs