[PATCH 0/2] Use multi-index entries in the page cache

["Matthew Wilcox (Oracle)" <willy@infradead.org>]

Following Hugh's advice at LSFMM 2019, I was trying to avoid doing this,
but it turns out to be hard to support range writeback with the pagecache
using multiple single entries.  Of course, this isn't a problem for
shmem because it doesn't have a real backing device (only swap), but
real filesystems need to start writeback at arbitrary file offsets and
have problems if we don't notice that the first (huge) page in the range
is dirty.

Hugh, I would love it if you could test this.  It didn't introduce any new
regressions to the xfstests, but shmem does exercise different paths and
of course I don't have a clean xfstests run yet, so there could easily
still be bugs.

I'd like this to be included in mmotm, but it is less urgent than the
previous patch series that I've sent.  As far as risk, I think it only
affects shmem/tmpfs.

Matthew Wilcox (Oracle) (2):
  XArray: Add xas_split
  mm: Use multi-index entries in the page cache

 Documentation/core-api/xarray.rst |  16 ++--
 include/linux/xarray.h            |   2 +
 lib/test_xarray.c                 |  41 ++++++++
 lib/xarray.c                      | 153 ++++++++++++++++++++++++++++--
 mm/filemap.c                      |  42 ++++----
 mm/huge_memory.c                  |  21 +++-
 mm/khugepaged.c                   |  12 ++-
 mm/shmem.c                        |  11 +--
 8 files changed, 245 insertions(+), 53 deletions(-)

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2.27.0