Implement arm64 specific huge_ptep_get()

Hi,

As Mike pointed out [1], the huge_ptep_get() will only return one specific pte value for the CONT-PTE or CONT-PMD size hugetlb on ARM64 system, which will not take into account the subpages' dirty or young bits of a CONT-PTE/PMD size hugetlb page. That will make us miss dirty or young flags of a CONT-PTE/PMD size hugetlb page for those functions that want to check the dirty or young flags of a hugetlb page. For example, the gather_hugetlb_stats() will get inaccurate dirty hugetlb page statistics, and the DAMON for hugetlb monitoring will also get inaccurate access statistics.

To fix this issue, this patch set introduces an ARM64 specific huge_ptep_get() implementation, which will take into account any subpages' dirty or young bits.

[1] https://lore.kernel.org/linux-mm/[email protected]/

Changes from v2:
- Fix some typos and update the commit message suggested by Anshuman.
- Improve some coding style issues.
- Add reviewed tag from Anshuman.

Changes from v1:
- Rebase on next-20220512.
- Update commit message suggested by Muchun.
- Add reviewed tag from Muchun.

Changes from RFC:
- Implement arm64 specific huge_ptep_get() instead of introducing a new interface.
- Add a new patch to convert huge_ptep_get() in hugetlbpage.c

Baolin Wang (2):
arm64/hugetlb: Use ptep_get() to get the pte value of a huge page arm64/hugetlb: Implement arm64 specific huge_ptep_get()

 arch/arm64/include/asm/hugetlb.h |  2 ++
 arch/arm64/mm/hugetlbpage.c      | 30 ++++++++++++++++++++++++++----
 2 files changed, 28 insertions(+), 4 deletions(-)

1.8.3.1