HAMMER cleanup

[Thomas Nikolajsen]

> > Anyway I think we should be able to choose *one* default cleanup strategy;
> > newbies won't have to worry and expert users will disable default and
> > impelment their own strategy anyway.
>
>Definitely.
>
>A simple yet versatile default strategy would be to run
>the cleanup in a nightly cronjob which stores the current
>date+time in a file somewhere.  Additionally, upon system

This is exactly what Sascha just commited.
`hammer cleanup' does save last time run in a file.

>boot a job is started in the background that first sleeps
>for half an hour (to avoid heavy I/O right after boot),
>then it checks the above mentioned file.  If there was no
>cleanup the previous night, it starts one right away.  A

This is exactly what I suggest to add;
`hammer cleanup' will only do work once in defined interval (default day).

You suggest 30 minutes delay after boot, which sounds good: many UPS
has battery for under 30 minutes, so after running for that period we will
most likely be running stable (ie. if using UPS, it should be well managed,
which will shut down system before powering off).

>similar check could be done when waking up from suspend.

A nice idea; I'm not sure we will tune for laptop use for DragonFly 2.2.
A proces continously monitoring need for pruning/reblocking will be
implemented later, I guess; this process could postpone pruning/reblocking
(but not snapshots, which are almost free to do) when laptop running on battery.

 -thomas