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Date:   Wed, 24 Oct 2018 15:56:39 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     Anshuman Khandual <anshuman.khandual@arm.com>
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
Subject: Re: [PATCH V3 3/5] mm/hugetlb: Enable arch specific huge page size
 support for migration
Message-ID: <20181024135639.GH18839@dhcp22.suse.cz>
References: <1540299721-26484-1-git-send-email-anshuman.khandual@arm.com>
 <1540299721-26484-4-git-send-email-anshuman.khandual@arm.com>
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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>

> ---
>  include/linux/hugetlb.h | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index 70bcd89..4cc3871 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -493,18 +493,29 @@ static inline pgoff_t basepage_index(struct page *page)
>  extern int dissolve_free_huge_page(struct page *page);
>  extern int dissolve_free_huge_pages(unsigned long start_pfn,
>  				    unsigned long end_pfn);
> -static inline bool hugepage_migration_supported(struct hstate *h)
> -{
> +
>  #ifdef CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION
> +#ifndef arch_hugetlb_migration_supported
> +static inline bool arch_hugetlb_migration_supported(struct hstate *h)
> +{
>  	if ((huge_page_shift(h) == PMD_SHIFT) ||
>  		(huge_page_shift(h) == PUD_SHIFT) ||
>  			(huge_page_shift(h) == PGDIR_SHIFT))
>  		return true;
>  	else
>  		return false;
> +}
> +#endif
>  #else
> +static inline bool arch_hugetlb_migration_supported(struct hstate *h)
> +{
>  	return false;
> +}
>  #endif
> +
> +static inline bool hugepage_migration_supported(struct hstate *h)
> +{
> +	return arch_hugetlb_migration_supported(h);
>  }
>  
>  /*
> -- 
> 2.7.4

-- 
Michal Hocko
SUSE Labs