On 10/04, Alexey Dobriyan wrote: > > On Tue, Oct 03, 2017 at 05:53:15PM +0200, Oleg Nesterov wrote: > > On 10/02, Andrew Morton wrote: > > > > > > From: Alexey Dobriyan <adobri...@gmail.com> > > > Subject: pid: delete RESERVED_PIDS > > > > > > RESERVED_PIDS had a noble goal: to protect root from PID exhaustion since > > > at least ~2.5.40 > > > > I am just curious, where did you find the change which documents this goal? > > Now that you asked, I'm not exactly sure. :-( Please don't tell it is for some > kind of stupid userspace which assumed low numbers are kernel threads.
Not necessarily kernel threads, > > > Allow small pids to be allocated after rollover, there is nothing sacred > > > about them. > > > > > > Resource exhaustion should be handled by rlimits and/or kernel memory > > > accounting. > > > > I won't argue, but I always thought that the only purpose of RESERVED_PIDS > > is to make the system/kernek daemons started at boot time more "visible" in > > /usr/bin/ps output. > > They will be first in line naturally: kthreadd + init execute first and > rarely exit. Exactly. But, with your patch, only until ->last_pid overlaps. And while I don't think this can break something, I bet humans will notice this change ;) And in fact, from time to time I thought that perhaps it makes sense to change alloc_pidmap() to check PF_KTHREAD and allocate the new pid from RESERVED_PIDS interval if it is set. So I am not sure this is change is really good but I won't argue. Oleg.