hugetlb: skip to end of PT page mapping when pte not present

Patch series "hugetlb: speed up linear address scanning", v2.

At unmap, fork and remap time hugetlb address ranges are linearly scanned.
We can optimize these scans if the ranges are sparsely populated.

Also, enable page table "Lazy copy" for hugetlb at fork.

NOTE: Architectures not defining CONFIG_ARCH_WANT_GENERAL_HUGETLB need to
add an arch specific version hugetlb_mask_last_page() to take advantage of
sparse address scanning improvements.  Baolin Wang added the routine for
arm64.  Other architectures which could be optimized are: ia64, mips,
parisc, powerpc, s390, sh and sparc.


This patch (of 4):

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.

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Mike Kravetz <[email protected]>
Tested-by: Baolin Wang <[email protected]>
Reviewed-by: Baolin Wang <[email protected]>
Acked-by: Muchun Song <[email protected]>
Reported-by: kernel test robot <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Peter Xu <[email protected]>
Cc: Naoya Horiguchi <[email protected]>
Cc: James Houghton <[email protected]>
Cc: Mina Almasry <[email protected]>
Cc: "Aneesh Kumar K.V" <[email protected]>
Cc: Anshuman Khandual <[email protected]>
Cc: Paul Walmsley <[email protected]>
Cc: Christian Borntraeger <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Rolf Eike Beer <[email protected]>
Cc: David Hildenbrand <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index c6cccfaf8708..ce30fad5fd13 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -194,6 +194,7 @@ pte_t *huge_pte_alloc(struct mm_struct *mm, struct vm_area_struct *vma,
 			unsigned long addr, unsigned long sz);
 pte_t *huge_pte_offset(struct mm_struct *mm,
 		       unsigned long addr, unsigned long sz);
+unsigned long hugetlb_mask_last_page(struct hstate *h);
 int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma,
 				unsigned long *addr, pte_t *ptep);
 void adjust_range_if_pmd_sharing_possible(struct vm_area_struct *vma,