I have noticed an annoying regression that was introduced in 4.2 and is still there in 4.4. mmap writes to FUSE filesystems are throttled down to basically zero.
Reproducer: https://github.com/rfjakob/mmapwrite , testing against encfs: $ mmapwrite /tmp/encfs-mnt/foo 1 .................................................. 107.01 MB/s 2 .................................................. 101.98 MB/s [...] 68 .................................................. 106.79 MB/s 69 .................................................. 105.09 MB/s 70 .................................................. 2.02 MB/s 71 .................................................. 1.77 MB/s 72 .................................................. 0.42 MB/s 73 .................................... (hangs) I have tested kernels from 4.0 and this seems to have been introduced in 4.2: 4.0 ....... 140MB/s permanent 4.1 ....... 140MB/s permanent 4.2 ....... 100MB/s at the start, sudden slowdown to 1MB/s after ~5GB 4.3 ....... 100MB/s at the start, sudden slowdown to 1MB/s after ~1.5GB 4.4-rc4 ... 100MB/s at the start, slowly ramps down, 0.3MB/s after ~2GB 4.4 ....... 100MB/s at the start, sudden slowdown after ~3GB Is there a way to disable the throttling? Or at least exempt FUSE until there is a proper fix? Thanks, Jakob
