Re: MAX_PID changes in 2.5.31

From: Linus Torvalds (
Date: Mon Aug 19 2002 - 15:06:35 EST

On Mon, 19 Aug 2002, Ingo Molnar wrote:
> The main problem is that there's the old-style SysV IPC interface that
> uses 16-bit PIDs still. All recent SysV applications (linked against glibc
> 2.2 or newer) use IPC_64, but any application linked against pre-2.2
> glibcs will fail. glibc 2.2 was released 2 years ago, is this enough of a
> timeout to obsolete the non-IPC_64 interfaces?

I actually did the pid changes partly to flush out problems spots, on
purpose making it 30 bits even though I actually eventually still think
that we may want to use a few bits for things like node ID numbers etc.

> if that is the case then can i rip all the non-IPC_64 parts out of ipc/*,
> and let non-IPC_64 calls fail? Right now it's silent breakage that
> happens.

Add a warning for now, the same way we did with stat() etc when moving to
64 bits.

> or, in my threading tree, i introduced a /proc/sys/kernel/pid_max tunable,
> which has the safe conservative value of 32K PIDs, but which can be
> changed by the admin to have higher PIDs.

Fair enough.


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