David Laight egy új algoritmust készített pid foglaláshz és a proc/pgrp feloldáshoz. A kód legfőbb erénye, hogy az id alapján történő feloldás nem igényel keresést, kisebb footprint-tel rendelkezik, skálázható, nem függ a MAXUSER-től, stb.
David levele:Subject: new pid allocation code
To: None
From: David Laight
List: tech-kern
Date: 03/11/2003 14:36:30
Hackers,
The code below implements a different pid allocation and proc/pgrp lookup algorithm.
The main benefits are:
- pid and pgrp lookup (by id) doesn't require a search
- no dependency on MAXUSERS
- automatically scales well to large numbers of processes
- small data footprint for small systems
- ability to enumerate through all the processes without holding a lock for the entire duration, or having very messy locking rules.
(the allproc list and p_list fields could be depracted later).
- Largely MP clean
The basic idea is to ensure that you allocate a pid number which references an empty slot in the lookup table. To do this a FIFO freelist is linked through the free slots of the lookup table. To avoid reusing pid numbers, the top bits of the pid are incremented each time the slot is reused (the last value is kept in the table). If the table is getting full (ie a pid would be reused in a relatively small number of forks), then the table size is doubled. Orphaned pgrps correctly stop the pid being reused, orphaned sessions keep the pgrp allocated.
Below is the main part of the change, there are other bits lurking in fork and exit. If people think this code is ok, I'll sort out a full diff against 'current' (and fix for sparc64).
(I've been running this code for months!)
David