From: "Aneesh Kumar K.V" <aneeshkumar.opensource@gmail.com>
To: Anshuman Khandual <anshuman.khandual@arm.com>,
Will Deacon <will.deacon@arm.com>,
"Kirill A. Shutemov" <kirill@shutemov.name>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
kirill.shutemov@linux.intel.com, akpm@linux-foundation.org,
mhocko@suse.com, zi.yan@cs.rutgers.edu
Subject: Re: [PATCH] mm/thp: Correctly differentiate between mapped THP and PMD migration entry
Date: Mon, 15 Oct 2018 14:02:48 +0530 [thread overview]
Message-ID: <4bf3951d-410f-fac4-dfb2-7dee5568e6ff@linux.ibm.com> (raw)
In-Reply-To: <fb0ee5dd-5799-f5af-891a-992dd9a16a9f@arm.com>
On 10/12/18 1:32 PM, Anshuman Khandual wrote:
>
>
> On 10/09/2018 06:48 PM, Will Deacon wrote:
>> On Tue, Oct 09, 2018 at 04:04:21PM +0300, Kirill A. Shutemov wrote:
>>> On Tue, Oct 09, 2018 at 09:28:58AM +0530, Anshuman Khandual wrote:
>>>> A normal mapped THP page at PMD level should be correctly differentiated
>>>> from a PMD migration entry while walking the page table. A mapped THP would
>>>> additionally check positive for pmd_present() along with pmd_trans_huge()
>>>> as compared to a PMD migration entry. This just adds a new conditional test
>>>> differentiating the two while walking the page table.
>>>>
>>>> Fixes: 616b8371539a6 ("mm: thp: enable thp migration in generic path")
>>>> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
>>>> ---
>>>> On X86, pmd_trans_huge() and is_pmd_migration_entry() are always mutually
>>>> exclusive which makes the current conditional block work for both mapped
>>>> and migration entries. This is not same with arm64 where pmd_trans_huge()
>>>> returns positive for both mapped and migration entries. Could some one
>>>> please explain why pmd_trans_huge() has to return false for migration
>>>> entries which just install swap bits and its still a PMD ?
>>>
>>> I guess it's just a design choice. Any reason why arm64 cannot do the
>>> same?
>>
>> Anshuman, would it work to:
>>
>> #define pmd_trans_huge(pmd) (pmd_present(pmd) && !(pmd_val(pmd) & PMD_TABLE_BIT))
> yeah this works but some how does not seem like the right thing to do
> but can be the very last option.
>
There can be other code paths that makes that assumption. I ended up
doing the below for pmd_trans_huge on ppc64.
/*
* Only returns true for a THP. False for pmd migration entry.
* We also need to return true when we come across a pte that
* in between a thp split. While splitting THP, we mark the pmd
* invalid (pmdp_invalidate()) before we set it with pte page
* address. A pmd_trans_huge() check against a pmd entry during that time
* should return true.
* We should not call this on a hugetlb entry. We should check for HugeTLB
* entry using vma->vm_flags
* The page table walk rule is explained in Documentation/vm/transhuge.rst
*/
static inline int pmd_trans_huge(pmd_t pmd)
{
if (!pmd_present(pmd))
return false;
if (radix_enabled())
return radix__pmd_trans_huge(pmd);
return hash__pmd_trans_huge(pmd);
}
-aneesh
next prev parent reply other threads:[~2018-10-15 8:32 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-09 3:58 [PATCH] mm/thp: Correctly differentiate between mapped THP and PMD migration entry Anshuman Khandual
2018-10-09 13:04 ` Kirill A. Shutemov
2018-10-09 13:18 ` Will Deacon
2018-10-12 8:02 ` Anshuman Khandual
2018-10-15 8:32 ` Aneesh Kumar K.V [this message]
2018-10-16 13:16 ` Anshuman Khandual
2018-10-09 13:42 ` Anshuman Khandual
2018-10-09 13:58 ` Zi Yan
2018-10-10 4:05 ` Anshuman Khandual
2018-10-10 12:43 ` Zi Yan
2018-10-12 8:00 ` Anshuman Khandual
2018-10-15 0:53 ` Zi Yan
2018-10-15 4:06 ` Anshuman Khandual
2018-10-16 14:31 ` Zi Yan
2018-10-18 2:17 ` Naoya Horiguchi
2018-11-02 5:22 ` Anshuman Khandual
2018-10-25 8:10 ` Anshuman Khandual
2018-10-25 18:45 ` Zi Yan
2018-10-26 1:39 ` Anshuman Khandual
2018-10-17 2:09 ` Andrea Arcangeli
2018-10-22 14:00 ` Zi Yan
2018-11-02 6:15 ` Anshuman Khandual
2018-11-06 0:35 ` Will Deacon
2018-11-06 9:51 ` Anshuman Khandual
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