The meaning of the `free` field is currently `zfs_arc_sys_free`, which
is the target amount of memory to leave free for the system, and is
constant after booting.
This commit changes the meaning of `free` to arc_free_memory(), the
amount of memory that the ARC considers to be free.
It also adds a new arcstat field `avail`, which tracks
`arc_available_memory()`.
Since `avail` can be negative, it also updates the arcstat script to
pretty-print negative values.
example output:
$ arcstat -f time,miss,arcsz,c,grow,need,free,avail 1
time miss arcsz c grow need free avail
15:03:02 39K 114G 114G 0 0 2.4G 407M
15:03:03 42K 114G 114G 0 0 2.1G 120M
15:03:04 40K 114G 114G 0 0 1.8G -177M
15:03:05 24K 113G 112G 0 0 1.7G -269M
15:03:06 29K 111G 110G 0 0 1.6G -385M
15:03:07 27K 110G 108G 0 0 1.4G -535M
15:03:08 13K 108G 108G 0 0 2.2G 239M
15:03:09 33K 107G 107G 0 0 1.3G -639M
15:03:10 16K 105G 102G 0 0 2.6G 704M
15:03:11 7.2K 102G 102G 0 0 5.1G 3.1G
15:03:12 42K 103G 102G 0 0 4.8G 2.8G
Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Pavel Zakharov <pavel.zakharov@delphix.com>
Reviewed-by: Tony Nguyen <tony.nguyen@delphix.com>
Signed-off-by: Matthew Ahrens <mahrens@delphix.com>
Closes#10494
7b232e9354