[PATCH v3 0/2] attempt to map anonymous pte-mapped THPs by pmds

[Xu Yu <xuyu@linux.alibaba.com>]

Result of tools/testing/selftests/mm/cow.c tests:
# [RUN] Basic COW after fork() when collapsing before fork()
ok 145 No leak from parent into child
# [RUN] Basic COW after fork() when collapsing after fork() (fully shared)
ok 146 No leak from parent into child
# [RUN] Basic COW after fork() when collapsing after fork() (lower shared)
ok 147 No leak from parent into child
# [RUN] Basic COW after fork() when collapsing after fork() (upper shared)
ok 148 No leak from parent into child

A long run (w/ CONFIG_DEBUG_VM enabled) shows no panic or memory leaks.

Changes since v2:
- Use folios in the new code, as suggested by David.
- Handle folio refcount and rmap properly, as suggested by David.
- minor modification includes 1) advance vma write lock, 2) remove
  redundant rollback logic, 3) clear old ptes in pgtable before deposit.

Changes since v1:
- Deal with PageAnonExclusive properly, as suggested by David.

Xu Yu (2):
  mm/khugepaged: map RO non-exclusive pte-mapped anon THPs by pmds
  mm/khugepaged: map exclusive anonymous pte-mapped THPs by pmds

 mm/khugepaged.c | 229 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 229 insertions(+)

-- 
2.37.1