RE: [patch] generic-pidhash-2.5.36-D4, BK-curr

From: Ingo Molnar (
Date: Fri Sep 20 2002 - 11:47:41 EST

On Fri, 20 Sep 2002, Hanumanthu. H wrote:

> First of all, using bitmap is not that good as exposed in this
> mailing list (I think some good guys at IBM already implememted
> bitmap for pids as part of Linux scalability enhancements & [...]

i mentioned that patch in earlier emails, and it is a whole different
thing. The patch built a completely new bitmap *every* time we hit an
already allocated PID, to find the next 'safe range'. The new PID
allocator in 2.5.37 keeps one bitmap and does a single set-bit map
operation in the fastpath and does a fast bitscan forward even in the
worst case.

> remember they discussed pros & cons too) & [...]

(that approach was pretty gross i have to say.)

> [...] atomic operations are not that cheap anyway. [...]



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