Re: [PATCH 1/4] hugetlb: skip to end of PT page mapping when pte not present

On Thu, Jun 16, 2022 at 02:05:15PM -0700, Mike Kravetz wrote:

HugeTLB address ranges are linearly scanned during fork, unmap and
remap operations.  If a non-present entry is encountered, the code
currently continues to the next huge page aligned address.  However,
a non-present entry implies that the page table page for that entry
is not present.  Therefore, the linear scan can skip to the end of
range mapped by the page table page.  This can speed operations on
large sparsely populated hugetlb mappings.

Create a new routine hugetlb_mask_last_page() that will return an
address mask.  When the mask is ORed with an address, the result
will be the address of the last huge page mapped by the associated
page table page.  Use this mask to update addresses in routines which
linearly scan hugetlb address ranges when a non-present pte is
encountered.

hugetlb_mask_last_page is related to the implementation of
huge_pte_offset as hugetlb_mask_last_page is called when huge_pte_offset
returns NULL.  This patch only provides a complete hugetlb_mask_last_page
implementation when CONFIG_ARCH_WANT_GENERAL_HUGETLB is defined.
Architectures which provide their own versions of huge_pte_offset can also
provide their own version of hugetlb_mask_last_page.

Signed-off-by: Mike Kravetz <redacted>
Tested-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>

It'll be more efficient, Thanks.

Acked-by: Muchun Song <redacted>