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[RFC PATCH 0/2] Add hstate parameter to huge_pte_offset()

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  [RFC PATCH 0/2] Add hstate parameter to huge_pte_offset() Punit Agrawal <punit.agrawal@arm.com> - 2017-03-23 14:00 +0100
    Re: [RFC PATCH 0/2] Add hstate parameter to huge_pte_offset() Mike Kravetz <mike.kravetz@oracle.com> - 2017-03-23 22:00 +0100
      Re: [RFC PATCH 0/2] Add hstate parameter to huge_pte_offset() "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-03-24 11:40 +0100
        Re: [RFC PATCH 0/2] Add hstate parameter to huge_pte_offset() Punit Agrawal <punit.agrawal@arm.com> - 2017-03-24 12:30 +0100

#1607456 — [RFC PATCH 0/2] Add hstate parameter to huge_pte_offset()

On architectures that support hugepages composed of contiguous pte as
well as block entries at the same level in the page table,
huge_pte_offset() is not able to determine the right offset to return
when it encounters a swap entry (which is used to mark poisoned as
well as migrated pages in the page table).

huge_pte_offset() needs to know the size of the hugepage at the
requested address to determine the offset to return - the current
entry or the first entry of a set of contiguous hugepages. This came
up while enabling support for memory failure handling on arm64[0].

Patch 1 adds a hstate parameter to huge_pte_offset() to provide
additional information about the target address. It also updates the
signatures (and usage) of huge_pte_offset() for architectures that
override the generic implementation. This patch has been compile
tested on ia64 and x86.

Patch 2 uses the size determined by the parameter added in Patch 1, to
return the correct page table offset.

The patchset is based on top of v4.11-rc3 and the arm64 huge page
cleanup for break-before-make[1].

Thanks,
Punit


[0] http://marc.info/?l=linux-arm-kernel&m=148772028907925&w=2
[1] https://www.spinics.net/lists/arm-kernel/msg570422.html

Punit Agrawal (2):
  mm/hugetlb.c: add hstate parameter to huge_pte_offset()
  arm64: hugetlbpages: Correctly handle swap entries in
    huge_pte_offset()

 arch/arm64/mm/hugetlbpage.c   | 33 +++++++++++++++++----------------
 arch/ia64/mm/hugetlbpage.c    |  4 ++--
 arch/metag/mm/hugetlbpage.c   |  2 +-
 arch/mips/mm/hugetlbpage.c    |  2 +-
 arch/parisc/mm/hugetlbpage.c  |  2 +-
 arch/powerpc/mm/hugetlbpage.c |  2 +-
 arch/s390/mm/hugetlbpage.c    |  2 +-
 arch/sh/mm/hugetlbpage.c      |  2 +-
 arch/sparc/mm/hugetlbpage.c   |  2 +-
 arch/tile/mm/hugetlbpage.c    |  2 +-
 arch/x86/mm/hugetlbpage.c     |  2 +-
 fs/userfaultfd.c              |  7 +++++--
 include/linux/hugetlb.h       |  2 +-
 mm/hugetlb.c                  | 18 +++++++++---------
 mm/page_vma_mapped.c          |  2 +-
 mm/pagewalk.c                 |  2 +-
 16 files changed, 45 insertions(+), 41 deletions(-)

-- 
2.11.0

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#1607905

On 03/23/2017 05:58 AM, Punit Agrawal wrote:
> On architectures that support hugepages composed of contiguous pte as
> well as block entries at the same level in the page table,
> huge_pte_offset() is not able to determine the right offset to return
> when it encounters a swap entry (which is used to mark poisoned as
> well as migrated pages in the page table).
> 
> huge_pte_offset() needs to know the size of the hugepage at the
> requested address to determine the offset to return - the current
> entry or the first entry of a set of contiguous hugepages. This came
> up while enabling support for memory failure handling on arm64[0].
> 
> Patch 1 adds a hstate parameter to huge_pte_offset() to provide
> additional information about the target address. It also updates the
> signatures (and usage) of huge_pte_offset() for architectures that
> override the generic implementation. This patch has been compile
> tested on ia64 and x86.

I haven't looked at the performance implications of making huge_pte_offset
just a little slower.  But, I think you can get hstate from the parameters
passed today.

vma = find_vma(mm, addr);
h = hstate_vma(vma);

-- 
Mike Kravetz

> Patch 2 uses the size determined by the parameter added in Patch 1, to
> return the correct page table offset.
> 
> The patchset is based on top of v4.11-rc3 and the arm64 huge page
> cleanup for break-before-make[1].
> 
> Thanks,
> Punit
> 
> 
> [0] http://marc.info/?l=linux-arm-kernel&m=148772028907925&w=2
> [1] https://www.spinics.net/lists/arm-kernel/msg570422.html
> 
> Punit Agrawal (2):
>   mm/hugetlb.c: add hstate parameter to huge_pte_offset()
>   arm64: hugetlbpages: Correctly handle swap entries in
>     huge_pte_offset()
> 
>  arch/arm64/mm/hugetlbpage.c   | 33 +++++++++++++++++----------------
>  arch/ia64/mm/hugetlbpage.c    |  4 ++--
>  arch/metag/mm/hugetlbpage.c   |  2 +-
>  arch/mips/mm/hugetlbpage.c    |  2 +-
>  arch/parisc/mm/hugetlbpage.c  |  2 +-
>  arch/powerpc/mm/hugetlbpage.c |  2 +-
>  arch/s390/mm/hugetlbpage.c    |  2 +-
>  arch/sh/mm/hugetlbpage.c      |  2 +-
>  arch/sparc/mm/hugetlbpage.c   |  2 +-
>  arch/tile/mm/hugetlbpage.c    |  2 +-
>  arch/x86/mm/hugetlbpage.c     |  2 +-
>  fs/userfaultfd.c              |  7 +++++--
>  include/linux/hugetlb.h       |  2 +-
>  mm/hugetlb.c                  | 18 +++++++++---------
>  mm/page_vma_mapped.c          |  2 +-
>  mm/pagewalk.c                 |  2 +-
>  16 files changed, 45 insertions(+), 41 deletions(-)
> 

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#1608302

On Thu, Mar 23, 2017 at 01:55:27PM -0700, Mike Kravetz wrote:
> On 03/23/2017 05:58 AM, Punit Agrawal wrote:
> > On architectures that support hugepages composed of contiguous pte as
> > well as block entries at the same level in the page table,
> > huge_pte_offset() is not able to determine the right offset to return
> > when it encounters a swap entry (which is used to mark poisoned as
> > well as migrated pages in the page table).
> > 
> > huge_pte_offset() needs to know the size of the hugepage at the
> > requested address to determine the offset to return - the current
> > entry or the first entry of a set of contiguous hugepages. This came
> > up while enabling support for memory failure handling on arm64[0].
> > 
> > Patch 1 adds a hstate parameter to huge_pte_offset() to provide
> > additional information about the target address. It also updates the
> > signatures (and usage) of huge_pte_offset() for architectures that
> > override the generic implementation. This patch has been compile
> > tested on ia64 and x86.
> 
> I haven't looked at the performance implications of making huge_pte_offset
> just a little slower.  But, I think you can get hstate from the parameters
> passed today.
> 
> vma = find_vma(mm, addr);
> h = hstate_vma(vma);

It's better to avoid find_vma() in fast(?) path if possible. So passing it
down is probably better.

-- 
 Kirill A. Shutemov

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#1608337

"Kirill A. Shutemov" <kirill@shutemov.name> writes:

> On Thu, Mar 23, 2017 at 01:55:27PM -0700, Mike Kravetz wrote:
>> On 03/23/2017 05:58 AM, Punit Agrawal wrote:
>> > On architectures that support hugepages composed of contiguous pte as
>> > well as block entries at the same level in the page table,
>> > huge_pte_offset() is not able to determine the right offset to return
>> > when it encounters a swap entry (which is used to mark poisoned as
>> > well as migrated pages in the page table).
>> > 
>> > huge_pte_offset() needs to know the size of the hugepage at the
>> > requested address to determine the offset to return - the current
>> > entry or the first entry of a set of contiguous hugepages. This came
>> > up while enabling support for memory failure handling on arm64[0].
>> > 
>> > Patch 1 adds a hstate parameter to huge_pte_offset() to provide
>> > additional information about the target address. It also updates the
>> > signatures (and usage) of huge_pte_offset() for architectures that
>> > override the generic implementation. This patch has been compile
>> > tested on ia64 and x86.
>> 
>> I haven't looked at the performance implications of making huge_pte_offset
>> just a little slower.  But, I think you can get hstate from the parameters
>> passed today.
>> 
>> vma = find_vma(mm, addr);
>> h = hstate_vma(vma);
>
> It's better to avoid find_vma() in fast(?) path if possible. So passing it
> down is probably better.

Also most call sites of huge_pte_offset() already have the hstate (or
the vma) readily available. So adding overhead feels unnecessary.

I agree that merging the patch will need some co-ordination but lets at
the least give it a shot.

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