From: Anshuman Khandual <anshuman.khandual@arm.com>
To: Will Deacon <will@kernel.org>
Cc: linux-mm@kvack.org, akpm@linux-foundation.org,
Catalin Marinas <catalin.marinas@arm.com>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH V2 1/3] arm64/mm: Drop __HAVE_ARCH_HUGE_PTEP_GET
Date: Wed, 6 May 2020 15:51:42 +0530 [thread overview]
Message-ID: <14911279-f800-a781-a4fd-de43215aa909@arm.com> (raw)
In-Reply-To: <20200506074315.GD7021@willie-the-truck>
On 05/06/2020 01:13 PM, Will Deacon wrote:
> On Wed, May 06, 2020 at 11:42:12AM +0530, Anshuman Khandual wrote:
>> Platform specific huge_ptep_get() is required only when fetching the huge
>> PTE involves more than just dereferencing the page table pointer. This is
>> not the case on arm64 platform. Hence huge_ptep_pte() can be dropped along
>> with it's __HAVE_ARCH_HUGE_PTEP_GET subscription.
>>
>> Cc: Catalin Marinas <catalin.marinas@arm.com>
>> Cc: Will Deacon <will@kernel.org>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: linux-arm-kernel@lists.infradead.org
>> Cc: linux-mm@kvack.org
>> Cc: linux-kernel@vger.kernel.org
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
>> ---
>> arch/arm64/include/asm/hugetlb.h | 6 ------
>> 1 file changed, 6 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/hugetlb.h b/arch/arm64/include/asm/hugetlb.h
>> index 2eb6c234d594..b88878ddc88b 100644
>> --- a/arch/arm64/include/asm/hugetlb.h
>> +++ b/arch/arm64/include/asm/hugetlb.h
>> @@ -17,12 +17,6 @@
>> extern bool arch_hugetlb_migration_supported(struct hstate *h);
>> #endif
>>
>> -#define __HAVE_ARCH_HUGE_PTEP_GET
>> -static inline pte_t huge_ptep_get(pte_t *ptep)
>> -{
>> - return READ_ONCE(*ptep);
>> -}
>
> Hmm, I'm nervous about dropping the READ_ONCE() here. We added them after
> running into page-table issues with THP [1] and it's really important to
> use them consistently to avoid hitting that again.
>
> If the generic code used READ_ONCE(), I'd be happy to switch to it.
Sure, will add READ_ONCE() in the generic huge_ptep_get(). AFAICS it should
not cause any problem for other platforms (but let me know otherwise).
>
> Will
>
> [1] https://lore.kernel.org/lkml/1506527369-19535-1-git-send-email-will.deacon@arm.com/
>
next prev parent reply other threads:[~2020-05-06 10:22 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-06 6:12 [PATCH V2 0/3] mm/hugetlb: Add some new generic fallbacks Anshuman Khandual
2020-05-06 6:12 ` [PATCH V2 1/3] arm64/mm: Drop __HAVE_ARCH_HUGE_PTEP_GET Anshuman Khandual
2020-05-06 7:43 ` Will Deacon
2020-05-06 10:21 ` Anshuman Khandual [this message]
2020-05-06 6:12 ` [PATCH V2 2/3] mm/hugetlb: Define a generic fallback for is_hugepage_only_range() Anshuman Khandual
2020-05-06 6:12 ` [PATCH V2 3/3] mm/hugetlb: Define a generic fallback for arch_clear_hugepage_flags() Anshuman Khandual
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