[REVIEW] unit number allocation API

[John Baldwin]

On Thursday 22 July 2004 01:38 pm, Julian Elischer wrote:
> Poul-Henning Kamp wrote:
> >We need to allocate unit numbers for (pseudo)devices, and a few
> >places we need to allocate inode numbers for synthetic filesystems
> >(for instance DEVFS).
> >
> >For these applications the overhead of rman(9) can be totally
> >unacceptable (60 bytes per allocation ?) and something more memory
> >frugal is called for.
> >
> >This is a small API I just wrote, targeted specifically for allocating
> >unit numbers and similar spaces.
> >
> >Currently the allocation policy is "lowest free number", but it
> >would be possible to add support for allocating a specific number
> >as well.
> >
> >It uses a mixed run-length/bitmap strategy with fixed size memory
> >chunks (so it can use uma(9) in the kernel).
> >
> >Worst case memory usage is two bits per managed unit-number (worst
> >case is "allocate all units, free all the odd numbered ones").
> >
> >For the typical case where we never free any unit numbers, it will
> >use 52 bytes in total on i386.
> >
> >Please review.  (It can be run in userland)
> >
> >Poul-Henning
>
> please also look at the Thread_id (lwpid) allocator marcel added to
> kern_thread.c

Whatever we use, can we use it to manage pids as well to work around the 
problem with putting newborn processes onto allproc.

-- 
John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org