Re: [REVIEW] unit number allocation API

From: John Baldwin (jhb_at_FreeBSD.org)
Date: 07/28/04

  • Next message: Dag-Erling Smørgrav: "Re: [REVIEW] unit number allocation API" 
    To: freebsd-arch@FreeBSD.org
Date: Tue, 27 Jul 2004 21:20:48 -0400

    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@FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org
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  • Next message: Dag-Erling Smørgrav: "Re: [REVIEW] unit number allocation API"

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    • Re: [REVIEW] unit number allocation API
      ... >(for instance DEVFS). ... >For these applications the overhead of rmancan be totally ... >This is a small API I just wrote, targeted specifically for allocating ...
      (freebsd-arch)
    • Re: [REVIEW] unit number allocation API
      ... >>places we need to allocate inode numbers for synthetic filesystems ... >>(for instance DEVFS). ... >>This is a small API I just wrote, targeted specifically for allocating ...
      (freebsd-arch)