fuse: support large folios

This patchset adds support for folios larger than one page size in FUSE.

This patchset is rebased on top of the (unmerged) patchset that removes temp
folios in writeback [1]. (There is also a version of this patchset that is
independent from that change, but that version has two additional patches
needed to account for temp folios and temp folio copying, which may require
some debate to get the API right for as these two patches add generic
(non-FUSE) helpers. For simplicity's sake for now, I sent out this patchset
version rebased on top of the patchset that removes temp pages)

This patchset was tested by running it through fstests on passthrough_hp.

Benchmarks show roughly a ~45% improvement in read throughput.

Benchmark setup:

-- Set up server --
 ./libfuse/build/example/passthrough_hp --bypass-rw=1 ~/libfuse
~/mounts/fuse/ --nopassthrough
(using libfuse patched with https://github.com/libfuse/libfuse/pull/807)

-- Run fio --
 fio --name=read --ioengine=sync --rw=read --bs=1M --size=1G
--numjobs=2 --ramp_time=30 --group_reporting=1
--directory=mounts/fuse/

Machine 1:
    No large folios:     ~4400 MiB/s
    Large folios:        ~7100 MiB/s

Machine 2:
    No large folios:     ~3700 MiB/s
    Large folios:        ~6400 MiB/s

Writes are still effectively one page size. Benchmarks showed that trying to get
the largest folios possible from __filemap_get_folio() is an over-optimization
and ends up being significantly more expensive. Fine-tuning for the optimal
order size for the __filemap_get_folio() calls can be done in a future patchset.

[1] https://lore.kernel.org/linux-fsdevel/20241107235614.3637...

Changelog:
v1: https://lore.kernel.org/linux-fsdevel/20241109001258.2216...
v1 -> v2:
* Change naming from "non-writeback write" to "writethrough write"
* Fix deadlock for writethrough writes by calling fault_in_iov_iter_readable() first
  before __filemap_get_folio() (Josef)
* For readahead, retain original folio_size() for descs.length (Josef)
* Use folio_zero_range() api in fuse_copy_folio() (Josef)
* Add Josef's reviewed-bys

Joanne Koong (12):
  fuse: support copying large folios
  fuse: support large folios for retrieves
  fuse: refactor fuse_fill_write_pages()
  fuse: support large folios for writethrough writes
  fuse: support large folios for folio reads
  fuse: support large folios for symlinks
  fuse: support large folios for stores
  fuse: support large folios for queued writes
  fuse: support large folios for readahead
  fuse: support large folios for direct io
  fuse: support large folios for writeback
  fuse: enable large folios

 fs/fuse/dev.c  | 128 ++++++++++++++++++++++++-------------------------
 fs/fuse/dir.c  |   8 ++--
 fs/fuse/file.c | 126 +++++++++++++++++++++++++++++++-----------------
 3 files changed, 149 insertions(+), 113 deletions(-)

-- 
2.43.5