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Subject: Re: [PATCH V3 3/5] mm/hugetlb: Enable arch specific huge page size
 support for migration
To:     Michal Hocko <mhocko@kernel.org>
Cc:     linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org, suzuki.poulose@arm.com,
        punit.agrawal@arm.com, will.deacon@arm.com, Steven.Price@arm.com,
        steve.capper@arm.com, catalin.marinas@arm.com,
        akpm@linux-foundation.org, mike.kravetz@oracle.com,
        n-horiguchi@ah.jp.nec.com
References: <1540299721-26484-1-git-send-email-anshuman.khandual@arm.com>
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 <20181024135639.GH18839@dhcp22.suse.cz>
 <20181024135859.GI18839@dhcp22.suse.cz>
From:   Anshuman Khandual <anshuman.khandual@arm.com>
Message-ID: <bf5e636c-9cc4-50d6-4160-78a1a7703860@arm.com>
Date:   Thu, 25 Oct 2018 11:53:34 +0530
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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@ah.jp.nec.com>
>>> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
>>
>> Acked-by: Michal Hocko <mhocko@use.com>
> 
> fat fingers here, should be mhocko@suse.com 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.