Re: [PATCH v2 09/12] mm: hwpoison: soft offline supports thp migration

[Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>]

On Thu, Nov 10, 2016 at 09:31:10PM +1100, Balbir Singh wrote:
> 
> 
> On 08/11/16 10:31, Naoya Horiguchi wrote:
> > This patch enables thp migration for soft offline.
> > 
> > Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> > ---
> >  mm/memory-failure.c | 31 ++++++++++++-------------------
> >  1 file changed, 12 insertions(+), 19 deletions(-)
> > 
> > diff --git v4.9-rc2-mmotm-2016-10-27-18-27/mm/memory-failure.c v4.9-rc2-mmotm-2016-10-27-18-27_patched/mm/memory-failure.c
> > index 19e796d..6cc8157 100644
> > --- v4.9-rc2-mmotm-2016-10-27-18-27/mm/memory-failure.c
> > +++ v4.9-rc2-mmotm-2016-10-27-18-27_patched/mm/memory-failure.c
> > @@ -1485,7 +1485,17 @@ static struct page *new_page(struct page *p, unsigned long private, int **x)
> >  	if (PageHuge(p))
> >  		return alloc_huge_page_node(page_hstate(compound_head(p)),
> >  						   nid);
> > -	else
> > +	else if (thp_migration_supported() && PageTransHuge(p)) {
> > +		struct page *thp;
> > +
> > +		thp = alloc_pages_node(nid,
> > +			(GFP_TRANSHUGE | __GFP_THISNODE) & ~__GFP_RECLAIM,
> > +			HPAGE_PMD_ORDER);
> > +		if (!thp)
> > +			return NULL;
> 
> Just wondering if new_page() fails, migration of that entry fails. Do we then
> split and migrate? I guess this applies to THP migration in general.

Yes, that's not implemented yet, but can be helpful.

I think that there are 2 types of callers of page migration,
one is a caller that specifies the target pages individually (like move_pages
and soft offline), and another is a caller that specifies the target pages
by (physical/virtual) address range basis.
Maybe the former ones want to fall back immediately to split and retry if
thp migration fails, and the latter ones want to retry thp migration more.
If this makes sense, we can make some more changes on retry logic to fit
the situation.

Thanks,
Naoya Horiguchi
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