Re: Linux 2.3.39 has 32bit uid. What about 32bit pid?

From: Khimenko Victor (khim@sch57.msk.ru)
Date: Sat Jan 15 2000 - 16:17:27 EST


In <UTC200001132346.AAA00310.aeb@arend.cwi.nl> Andries.Brouwer@cwi.nl (Andries.Brouwer@cwi.nl) wrote:
>>> Thus, if we change get_pid() so as to use pids larger than 32000
>>> we need CONFIG_15BIT_PID (default=n) so that people who cannot or
>>> do not want to recompile their ipc using stuff can use a new kernel.

>> /proc/sys/kern/max_pid ?

> I do not think that would be meaningful.

It WOULD BE. Think about clusters. With 32bit pids you can use 8bit to identify
node and 24bit to identify task on that node. To do this you'll need
max_pid==16777215 (or max_pid==8388607 ? whatever... plus few reserved pids
can be handy sometimes). IMHO max_pid is exactly right here.

> A new distribution comes with recompiled applications.
> People installing things themselves can choose between
> recompiling the applications or configuring with CONFIG_15BIT_PID.
> If the default is to use 31 bits instead of 15 bits, then I cannot
> see any need for dynamically adjusting max_pid.

See above.

> (And I would prefer things to be right by default, not that we
> all have to add stuff to our rc scripts with
> echo 2147483647 > /proc/sys/kern/max_pid
> or so. Before you know it this will grow into an entire industry,
> with scripts trying to determine whether some old ipc using stuff
> still exists, and to use an appropriate echo.)

Default should be 31bit IMO but sometimes you need something other.
Since max_pid access is not very time critical adjustable max value will
be good.

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