[0/2] mm,thp: Add filemap_huge_fault() for THP

Message

William Kucharski July 28, 2019, 10:47 p.m. UTC

This set of patches is the first step towards a mechanism for automatically
mapping read-only text areas of appropriate size and alignment to THPs whenever
possible.

For now, the central routine, filemap_huge_fault(), amd various support
routines are only included if the experimental kernel configuration option

	RO_EXEC_FILEMAP_HUGE_FAULT_THP

is enabled.

This is because filemap_huge_fault() is dependent upon the
address_space_operations vector readpage() pointing to a routine that
will read and fill an entire large page at a time without poulluting the
page cache with PAGESIZE entries for the large page being mapped or
performing readahead that would pollute the page cache entries for
succeeding large pages. Unfortunately, there is no good way to determine
how many bytes were read by readpage(). At present, if filemap_huge_fault()
were to call a conventional readpage() routine, it would only fill the first
PAGESIZE bytes of the large page, which is definitely NOT the desired behavior.

However, by making the code available now it is hoped that filesystem
maintainers who have pledged to provide such a mechanism will do so more
rapidly.

The first part of the patch adds an order field to __page_cache_alloc(),
allowing callers to directly request page cache pages of various sizes.
This code was provided by Matthew Wilcox.

The second part of the patch implements the filemap_huge_fault() mechanism as
described above.

Matthew Wilcox (1):
  mm: Allow the page cache to allocate large pages

William Kucharski (2):
  mm: Allow the page cache to allocate large pages
  mm,thp: Add config experimental option RO_EXEC_FILEMAP_HUGE_FAULT_THP

 fs/afs/dir.c            |   2 +-
 fs/btrfs/compression.c  |   2 +-
 fs/cachefiles/rdwr.c    |   4 +-
 fs/ceph/addr.c          |   2 +-
 fs/ceph/file.c          |   2 +-
 include/linux/huge_mm.h |  16 +-
 include/linux/mm.h      |   6 +
 include/linux/pagemap.h |  13 +-
 mm/Kconfig              |  15 ++
 mm/filemap.c            | 322 ++++++++++++++++++++++++++++++++++++++--
 mm/huge_memory.c        |   3 +
 mm/mmap.c               |  36 ++++-
 mm/readahead.c          |   2 +-
 mm/rmap.c               |   8 +
 net/ceph/pagelist.c     |   4 +-
 net/ceph/pagevec.c      |   2 +-
 16 files changed, 404 insertions(+), 35 deletions(-)