Messages in this thread | | | Subject | Re: pid_t range question | From | (Eric W. Biederman) | Date | Thu, 09 Feb 2006 11:11:56 -0700 |
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Jan Engelhardt <jengelh@linux01.gwdg.de> writes:
>>> On Linux, type pid_t is defined as an int if you look >>> through all the intermediate definitions such as S32_T, >>> etc. However, it wraps at 32767, the next value being 300. > > There is also an aesthetical reason. If pids were allowed to exceed, say, > ten million, you would need a quite wide field in `ps` for the process > number which is on "normal desktop user" systems just require 5 or 6 > decimal places. Well, what I mean, just look at this sample ps output: > > 17:59 shanghai:../fs/proc # ps > PID TTY TIME CMD > 1 - 00:00:00 init [3] > 4215914607 tty2 00:00:00 bash > 4215914653 tty2 00:00:00 ps > > mingw/msys and cygwin already have this "cosmetic problem" since windows > "pids" are usually above one million.
Yes. Although this I'm not I'm not certain how bad the cosmetic problem is. Certainly significant enough that we don't want to change a good thing when we got it. But if there were real problems a big pid would solve I don't expect large pid numbers to stop us.
>>> I know the >>> code "reserves" the first 300 pids. > > I cannot confirm that. When I start in "-b" mode and 'use' up all pids by > repeatedly executing /bin/noop, I someday get pids as low as 10 > again, defined by how many kernel threads there are active before /bin/bash > started.
Odd. When the search wraps it starts searching at 300. Still there are no locks around last_pid.
>>I know for certain that proc assumes it can fit pid in >>the upper bits of an ino_t taking the low 16bits for itself >>so that may the entire reason for the limit. >> > inode number in /proc/XXX/fd creation currently is, IIRC > ino = (pid << 16) | fd > which limits both pid to 16 bits and the fdtable to 16 bits. See > fs/proc/inode-alloc.txt. At best, procfs should start using 64bit inode > numbers.
Well it does use 64bit inode numbers but only on 64bit systems. Internally /proc doesn't care about the inode it is only for keep find and friends from getting confused.
Figuring out how to use find_inode_number would likely be interesting, and a random inode allocation scheme would be interesting.
Eric
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