Some more information. 1) On my machine, reading the temperature using, say, yacpi, causes one processor to process all the pending ACPI events. On a uniprocessor machine, the machine would appear to hang for several seconds; not so on my dual-core machine :)
2) The lare slab usage (1.1 Gb) was in part due to the XFS cache data; all three of my machine's filesystems are XFS. So the Acpi-State line in /proc/slabinfo is the really meaningful one. Here is my complete log so far, with annotations. 2006-06-21T20:06:10: Slab: 30296 kB 2006-17-21T20:17:01: Slab: 37756 kB 2006-17-21T21:17:01: Slab: 48116 kB 2006-17-21T22:17:01: Slab: 55764 kB 2006-17-21T23:17:01: Slab: 69904 kB -- Reboot with acpi=noirq: only one CPU found -- 2006-24-21T23:24:10: Slab: 10444 kB -- Reboot with pci=noacpi: only one CPU found -- 2006-30-21T23:30:26: Slab: 9676 kB 2006-30-21T23:30:26: Acpi-State 0 0 80 48 1 : tunables 120 60 8 : slabdata 0 0 0 -- Reboot with no options: OK, both CPUs found -- 2006-34-21T23:34:23: Slab: 10584 kB 2006-34-21T23:34:23: Acpi-State 0 0 80 48 1 : tunables 120 60 8 : slabdata 0 0 0 2006-17-22T00:17:01: Slab: 15424 kB 2006-17-22T00:17:01: Acpi-State 23088 23088 80 48 1 : tunables 120 60 8 : slabdata 481 481 0 2006-17-22T01:17:01: Slab: 29956 kB 2006-17-22T01:17:01: Acpi-State 59136 59136 80 48 1 : tunables 120 60 8 : slabdata 1232 1232 0 2006-17-22T02:17:01: Slab: 37764 kB 2006-17-22T02:17:01: Acpi-State 95088 95088 80 48 1 : tunables 120 60 8 : slabdata 1981 1981 0 2006-17-22T03:17:01: Slab: 45544 kB 2006-17-22T03:17:01: Acpi-State 130992 130992 80 48 1 : tunables 120 60 8 : slabdata 2729 2729 0 2006-17-22T04:17:01: Slab: 53328 kB 2006-17-22T04:17:01: Acpi-State 166944 166944 80 48 1 : tunables 120 60 8 : slabdata 3478 3478 0 2006-17-22T05:17:01: Slab: 61120 kB 2006-17-22T05:17:01: Acpi-State 202896 202896 80 48 1 : tunables 120 60 8 : slabdata 4227 4227 0 2006-17-22T06:17:01: Slab: 68904 kB 2006-17-22T06:17:01: Acpi-State 238800 238800 80 48 1 : tunables 120 60 8 : slabdata 4975 4975 0 2006-17-22T07:17:01: Slab: 1152624 kB 2006-17-22T07:17:01: Acpi-State 274656 274656 80 48 1 : tunables 120 60 8 : slabdata 5722 5722 0 2006-17-22T08:17:01: Slab: 1160376 kB 2006-17-22T08:17:01: Acpi-State 310608 310608 80 48 1 : tunables 120 60 8 : slabdata 6471 6471 0 2006-17-22T09:17:01: Slab: 1168168 kB 2006-17-22T09:17:01: Acpi-State 346464 346464 80 48 1 : tunables 120 60 8 : slabdata 7218 7218 0 2006-17-22T10:17:01: Slab: 1175892 kB 2006-17-22T10:17:01: Acpi-State 382176 382176 80 48 1 : tunables 120 60 8 : slabdata 7962 7962 0 2006-17-22T11:17:01: Slab: 1183660 kB 2006-17-22T11:17:01: Acpi-State 417984 417984 80 48 1 : tunables 120 60 8 : slabdata 8708 8708 0 2006-17-22T12:17:01: Slab: 1191400 kB 2006-17-22T12:17:01: Acpi-State 453744 453744 80 48 1 : tunables 120 60 8 : slabdata 9453 9453 0 2006-17-22T13:17:01: Slab: 1202924 kB 2006-17-22T13:17:01: Acpi-State 489696 489696 80 48 1 : tunables 120 60 8 : slabdata 10202 10202 0 -- Start yacpi, monitoring the temperature every second. -- Note how the slab allocation drops by ~100M and then stays constant. 2006-17-22T14:17:01: Slab: 1097584 kB 2006-17-22T14:17:01: Acpi-State 109 144 80 48 1 : tunables 120 60 8 : slabdata 3 3 0 2006-17-22T15:17:01: Slab: 1097532 kB 2006-17-22T15:17:01: Acpi-State 45 96 80 48 1 : tunables 120 60 8 : slabdata 2 2 0 2006-17-22T16:17:01: Slab: 1097536 kB 2006-17-22T16:17:01: Acpi-State 75 144 80 48 1 : tunables 120 60 8 : slabdata 3 3 0 2006-17-22T17:17:01: Slab: 1097668 kB 2006-17-22T17:17:01: Acpi-State 141 144 80 48 1 : tunables 120 60 8 : slabdata 3 3 0 -- Stop the yacpi monitoring. 2006-17-22T18:17:01: Slab: 1098904 kB 2006-17-22T18:17:01: Acpi-State 5808 5808 80 48 1 : tunables 120 60 8 : slabdata 121 121 0 -- At this point the Acpi-State has started increasing again, but is still -- small. Most of the slab allocations are in the XFS caches (all three -- filesystems on this computer are XFS). -- To make sure the memory can be released, start a fairly large compilation -- using both CPUs and 2x370 M of RAM. Just before compilation: 2006-48-22T18:48:56: Slab: 1103244 kB 2006-48-22T18:48:56: Acpi-State 24528 24528 80 48 1 : tunables 120 60 8 : slabdata 511 511 0 -- A couple of minutes into the compilation, the fans have still not turned on -- and the CPU is getting so hot it burns my hand. Restart yacpi, monitoring -- temperature every second. The temp is 85°C (dangerous!!) One CPU starts -- processing the backlog of ACPI events, the other continues the compilation. -- Fans start. Temperature drops to 71°C and stays there. 2006-00-22T19:00:44: Slab: 861828 kB 2006-00-22T19:00:44: Acpi-State 74 96 80 48 1 : tunables 120 60 8 : slabdata 2 2 0 -- End of compilation. During the final packaging stages, the temperature has -- dropped to 57°C as the CPUs were less used. Stop the yacpi monitoring. 2006-07-22T19:07:13: Slab: 865660 kB 2006-07-22T19:07:13: Acpi-State 73 96 80 48 1 : tunables 120 60 8 : slabdata 2 2 0 2006-17-22T19:17:01: Slab: 865028 kB 2006-17-22T19:17:01: Acpi-State 71 144 80 48 1 : tunables 120 60 8 : slabdata 3 3 0 2006-17-22T20:17:01: Slab: 871224 kB 2006-17-22T20:17:01: Acpi-State 34704 34704 80 48 1 : tunables 120 60 8 : slabdata 723 723 0 2006-17-22T21:17:01: Slab: 879112 kB 2006-17-22T21:17:01: Acpi-State 69552 69552 80 48 1 : tunables 120 60 8 : slabdata 1449 1449 0 2006-17-22T22:17:01: Slab: 887908 kB 2006-17-22T22:17:01: Acpi-State 104784 104784 80 48 1 : tunables 120 60 8 : slabdata 2183 2183 0 2006-17-22T23:17:01: Slab: 896024 kB 2006-17-22T23:17:01: Acpi-State 139920 139968 80 48 1 : tunables 120 60 8 : slabdata 2915 2916 0