Re: [RFC] [PATCH 00/13] Introduce task_pid api

From: Paul Jackson
Date: Wed Nov 16 2005 - 16:07:18 EST

> Could we switch
> to 128-bits so that pids are never reused or something like that?

Not easily. We've got a very cool pid-dispenser at this point that
has excellent performance and scalability, but requires a bit map,
one bit per potential pid. That bitmap can't exceed a small percentage
of main memory on most any configuration, constraining us to perhaps
20 to 30 bits. The code currently has a 22 bit arbitrary limit.
Something like 30 bits would usually only make sense on the terabyte
NUMA monster boxes.

128-bit UUID technology scales fine, but adds quite a few compute
cycles per allocation, and would blow out a whole lot of user code
expecting to put a pid in a machine word.

I won't rest till it's the best ...
Programmer, Linux Scalability
Paul Jackson <pj@xxxxxxx> 1.925.600.0401
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