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Date:   Wed, 24 Oct 2018 15:58:59 +0200
From:   Michal Hocko <>
To:     Anshuman Khandual <>
Subject: Re: [PATCH V3 3/5] mm/hugetlb: Enable arch specific huge page size
 support for migration

On Wed 24-10-18 15:56:39, Michal Hocko wrote:
> On Tue 23-10-18 18:31:59, Anshuman Khandual wrote:
> > Architectures like arm64 have HugeTLB page sizes which are different than
> > generic sizes at PMD, PUD, PGD level and implemented via contiguous bits.
> > At present these special size HugeTLB pages cannot be identified through
> > macros like (PMD|PUD|PGDIR)_SHIFT and hence chosen not be migrated.
> > 
> > Enabling migration support for these special HugeTLB page sizes along with
> > the generic ones (PMD|PUD|PGD) would require identifying all of them on a
> > given platform. A platform specific hook can precisely enumerate all huge
> > page sizes supported for migration. Instead of comparing against standard
> > huge page orders let hugetlb_migration_support() function call a platform
> > hook arch_hugetlb_migration_support(). Default definition for the platform
> > hook maintains existing semantics which checks standard huge page order.
> > But an architecture can choose to override the default and provide support
> > for a comprehensive set of huge page sizes.
> > 
> > Reviewed-by: Naoya Horiguchi <>
> > Signed-off-by: Anshuman Khandual <>
> Acked-by: Michal Hocko <>

fat fingers here, should be of course.
Michal Hocko

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