Re: [PATCH] Linux-2.5 fix/improve get_pid()

["H. Peter Anvin" <hpa@zytor.com>]

Followup to:  <Pine.LNX.4.44.0208081312330.8705-100000@home.transmeta.com>
By author:    Linus Torvalds <torvalds@transmeta.com>
In newsgroup: linux.dev.kernel
> 
> Guys, this discussion is getting ridiculous.
> 
> Doing a bit allocator should be trivial, but it's hard to know when a bit
> is to be free'd. You can't just do it at "exit()" time, because even if
> pid X exits, that doesn't mean that X can be re-used: it may still be used
> as a pgid or a tid by some other process Y.
> 
> So if you really want to take this approach, you need to count the uses of
> "pid X", and free the bitmap entry only when that count goes to zero. I
> see no such logic in Bill Irwin's code, only a comment about last use
> (which doesn't explain how to notice that last use).
> 

Even so, we need to maintain Not Recently Used semantic.  A discussion
on #kernel seems to have ended up with recommending a design target of
"no pid reuse within 30 seconds", with 1 second being an absolute
requirement.

	-hpa
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