fusefrontend: coalesce 4kB writes
This improves performance on hdds running ext4, and improves
streaming write performance on hdds running btrfs. Tar extract
slows down on btrfs for some reason.
See https://github.com/rfjakob/gocryptfs/issues/63
Benchmarks:
encfs v1.9.1
============
$ ./benchmark.bash -encfs /mnt/hdd-ext4
Testing EncFS at /mnt/hdd-ext4/benchmark.bash.u0g
WRITE: 131072000 bytes (131 MB, 125 MiB) copied, 1,48354 s, 88,4 MB/s
UNTAR: 20.79
LS: 3.04
RM: 6.62
$ ./benchmark.bash -encfs /mnt/hdd-btrfs
Testing EncFS at /mnt/hdd-btrfs/benchmark.bash.h40
WRITE: 131072000 bytes (131 MB, 125 MiB) copied, 1,52552 s, 85,9 MB/s
UNTAR: 24.51
LS: 2.73
RM: 5.32
gocryptfs v1.1.1-26-g4a7f8ef
============================
$ ./benchmark.bash /mnt/hdd-ext4
Testing gocryptfs at /mnt/hdd-ext4/benchmark.bash.1KG
WRITE: 131072000 bytes (131 MB, 125 MiB) copied, 1,55782 s, 84,1 MB/s
UNTAR: 22.23
LS: 1.47
RM: 4.17
$ ./benchmark.bash /mnt/hdd-btrfs
Testing gocryptfs at /mnt/hdd-btrfs/benchmark.bash.2t8
WRITE: 131072000 bytes (131 MB, 125 MiB) copied, 6,87206 s, 19,1 MB/s
UNTAR: 69.87
LS: 1.52
RM: 5.33
gocryptfs v1.1.1-32
===================
$ ./benchmark.bash /mnt/hdd-ext4
Testing gocryptfs at /mnt/hdd-ext4/benchmark.bash.Qt3
WRITE: 131072000 bytes (131 MB, 125 MiB) copied, 1,22577 s, 107 MB/s
UNTAR: 23.46
LS: 1.46
RM: 4.67
$ ./benchmark.bash /mnt/hdd-btrfs/
Testing gocryptfs at /mnt/hdd-btrfs//benchmark.bash.XVk
WRITE: 131072000 bytes (131 MB, 125 MiB) copied, 3,68735 s, 35,5 MB/s
UNTAR: 116.87
LS: 1.84
RM: 6.34
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