[v3,0/2] Implement arm64 specific huge_ptep_get()

Message

Baolin Wang May 16, 2022, 12:55 a.m. UTC

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/[e-mail]/

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(-)

Comments

Catalin Marinas May 16, 2022, 10:53 p.m. UTC | #1

On Mon, 16 May 2022 08:55:56 +0800, Baolin Wang wrote:
> 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.
> 
> [...]

Applied to arm64 (for-next/misc), thanks!

[1/2] arm64/hugetlb: Use ptep_get() to get the pte value of a huge page
      https://git.kernel.org/arm64/c/f0d9d79ec793
[2/2] arm64/hugetlb: Implement arm64 specific huge_ptep_get()
      https://git.kernel.org/arm64/c/bc5dfb4fd7bd