No subject

https://patrick-nagel.net/blog/archives/337
 "I did it three times with and three times without the =E2=80=9Cdiscar=
d=E2=80=9D
  option, and then took the average of those three tries:
  Without =E2=80=9Cdiscard=E2=80=9D option:
      Unpack: 1.21s
      Sync: 1.66s (=3D 172 MB/s)
      Delete: 0.47s
      Sync: 0.17s
  With =E2=80=9Cdiscard=E2=80=9D option:
      Unpack: 1.18s
      Sync: 1.62s (=3D 176 MB/s)
      Delete: 0.48s
      Sync: 40.41s
  So, with =E2=80=9Cdiscard=E2=80=9D on, deleting a big bunch of small =
files is 64
  times slower on my SSD. For those ~40 seconds any I/O is really
  slow, so that=E2=80=99s pretty much the time when you get a fresh cup=
 of
  coffee, or waste time watching the mass storage activity LED."

Also the 'man' page for 'fstrim':

http://www.vdmeulen.net/cgi-bin/man/man2html=3Ffstrim+8
 "-m, --minimum minimum-free-extent
    Minimum contiguous free range to discard, in bytes.
    (This value is internally rounded up to a multiple of the
    filesystem block size). Free ranges smaller than this will be
    ignored. By increasing this value, the fstrim operation will
    complete more quickly for filesystems with badly fragmented
    freespace, although not all blocks will be discarded. Default
    value is zero, discard every free block."

Note the "By increasing this value, the fstrim operation will
complete more quickly for filesystems with badly fragmented
freespace", which implies that FITRIM is also synchronous or slow
or both.