Re: [PATCH V3 3/5] mm/hugetlb: Enable arch specific huge page size support for migration

From: Anshuman Khandual
Date: Thu Oct 25 2018 - 02:23:49 EST

On 10/24/2018 07:28 PM, Michal Hocko wrote:
> 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 <n-horiguchi@xxxxxxxxxxxxx>
>>> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
>> Acked-by: Michal Hocko <mhocko@xxxxxxx>
> fat fingers here, should be mhocko@xxxxxxxx of course.

Sure no problems. As we had discussed earlier and agreed to keep the previous
patch "mm/hugetlb: Enable PUD level huge page migration" separate and not fold
into this one, I will assume your ACK on it as well unless your disagree.