fuse: enable large folios

Enable large folios, capping the max order at the largest request fuse
can issue, so a folio always fits within a single request. The order
range minimum is 0, so under memory pressure the allocator falls back to
smaller folios.

Benchmarks (libfuse passthrough_hp, buffered fio, single job, 4 GiB
file, medians, NUMA-pinned, performance governor, strictlimiting on by
default):

tmpfs backing (page-cache bound):
  workload          bs      large folios off   on        delta
  seq read,  cold,  128k    3110 MiB/s    4514 MiB/s     +45%
  seq read,  cold,  1M      3079 MiB/s    5181 MiB/s     +68%
  seq read,  warm,  128k    2438 MiB/s    4486 MiB/s     +84%
  seq read,  warm,  1M      2403 MiB/s    5123 MiB/s    +113%
  writeback write, seq,128k 1211 MiB/s    1699 MiB/s     +40%
  writeback write, seq, 1M  1462 MiB/s    2208 MiB/s     +51%
  writeback write, rand,128k 1101 MiB/s   1757 MiB/s     +60% +
  writeback write, rand, 1M 1284 MiB/s    2228 MiB/s     +74% +

xfs on NVMe backing (device bound for cold I/O):
  workload          bs      large folios off   on        delta
  seq read,  cold,  128k    2030 MiB/s    2172 MiB/s      +7% *
  seq read,  cold,  1M      1999 MiB/s    2181 MiB/s      +9% *
  seq read,  warm,  128k    2451 MiB/s    4939 MiB/s    +101%
  seq read,  warm,  1M      2340 MiB/s    5639 MiB/s    +141%
  writeback write, seq,128k  637 MiB/s     747 MiB/s     +17% *
  writeback write, seq, 1M   694 MiB/s     833 MiB/s     +20% *
  writeback write, rand,128k 1004 MiB/s   1648 MiB/s     +64% +
  writeback write, rand, 1M 1171 MiB/s    2055 MiB/s     +75% +

(*) device-bandwidth bound. Not much throughput gain but system cpu
utilization was roughly halved
(+) random write was tested as an overwrite of a hot region (under
writeback, this is page-cache bound, so the gain comes from lower
per-folio cpu overhead rather than higher backing-device throughput)

Random reads (4k and 128k) and writethrough writes were neutral with
no regression (no read-modify-write or read-amplification penalty from
large folios)

More information about the benchmark setup and results are in
https://github.com/joannekoong/linux/commits/fuse_large_folios_benchmarks/

Reviewed-by: Horst Birthelmer <hbirthelmer@ddn.com>
Reviewed-by: Jingbo Xu <jefflexu@linux.alibaba.com>
Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

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