Re: + mm-madvise-enable-soft-offline-of-hugetlb-pages-at-pud-level.patch added to -mm tree

[Alexandru Moise <00moses.alexander00@gmail.com>]

On Tue, Oct 03, 2017 at 09:33:01AM +0200, Michal Hocko wrote:
> I am sorry to jump here late
> 
> On Thu 28-09-17 14:43:24, Andrew Morton wrote:
> > From: Alexandru Moise <00moses.alexander00@gmail.com>
> > Subject: mm/madvise: enable soft offline of HugeTLB pages at PUD level
> > 
> > Since 94310cbcaa3c2 ("mm/madvise: enable (soft|hard) offline of HugeTLB
> > pages at PGD level") we've been able to soft offline 1G hugepages at the
> > PGD level, however x86_64 gigantic hugepages are at the PUD level so we
> > should add an extra check to account for hstate order at PUD level.
> > 
> > I'm not sure if this also applies to 5 level page tables on x86_64
> > however. Tested with 4 level pagetable.
> 
> This patch is wrong I believe! And I suspect 94310cbcaa3c2 is wrong as
> well but I am not familiar with ppc enough to be sure. It will allow
> PUD, PGD pages to be allocated from the zone movable while at least PUD
> pages are not migrateable for x86_64 AFAIR. Are PGD pages migrateable
> on ppc? If yes, are there any other architectures to allow PGD hugetlb
> pages which are not migrateable?
> 
> Andrew, could you drop it please?
>  

What exactly makes it wrong? When I tested this I saw no failure,
copy_huge_page() seems to take into account gigantic hugepages,
and when you move the mapping you don't really care about the
page size?

../Alex

> > Link: http://lkml.kernel.org/r/20170913101047.GA13026@gmail.com
> > Signed-off-by: Alexandru Moise <00moses.alexander00@gmail.com>
> > Cc: Michal Hocko <mhocko@suse.com>
> > Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> > Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> > Cc: Mike Kravetz <mike.kravetz@oracle.com>
> > Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com>
> > Cc: Punit Agrawal <punit.agrawal@arm.com>
> > Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>
> > Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
> > Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> > ---
> > 
> >  include/linux/hugetlb.h |    1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff -puN include/linux/hugetlb.h~mm-madvise-enable-soft-offline-of-hugetlb-pages-at-pud-level include/linux/hugetlb.h
> > --- a/include/linux/hugetlb.h~mm-madvise-enable-soft-offline-of-hugetlb-pages-at-pud-level
> > +++ a/include/linux/hugetlb.h
> > @@ -480,6 +480,7 @@ static inline bool hugepage_migration_su
> >  {
> >  #ifdef CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION
> >  	if ((huge_page_shift(h) == PMD_SHIFT) ||
> > +		(huge_page_shift(h) == PUD_SHIFT) ||
> >  		(huge_page_shift(h) == PGDIR_SHIFT))
> >  		return true;
> >  	else
> > _
> > 
> > Patches currently in -mm which might be from 00moses.alexander00@gmail.com are
> > 
> > mm-hugetlb-soft_offline-save-compound-page-order-before-page-migration.patch
> > mm-madvise-enable-soft-offline-of-hugetlb-pages-at-pud-level.patch
> > 
> 
> -- 
> Michal Hocko
> SUSE Labs

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