(switched to email. Please respond via emailed reply-to-all, not via the bugzilla web interface). I'm not sure who to blame here so I'll just spray it at everyone I've ever met ;) On Thu, 16 Dec 2010 23:00:12 GMT bugzilla-daemon@xxxxxxxxxxxxxxxxxxx wrote: > https://bugzilla.kernel.org/show_bug.cgi?id=25042 > > Summary: RAM buffer I/O resource badly interacts with memory > hot-add > Product: Memory Management > Version: 2.5 > Kernel Version: 2.6.35 > Platform: All > OS/Version: Linux > Tree: Mainline > Status: NEW > Severity: normal > Priority: P1 > Component: Other > AssignedTo: akpm@xxxxxxxxxxxxxxxxxxxx > ReportedBy: petr@xxxxxxxxxxxxxx > CC: akataria@xxxxxxxxxx > Regression: Yes > > > Created an attachment (id=40502) > --> (https://bugzilla.kernel.org/attachment.cgi?id=40502) > /proc/iomem after issuing hot-add, one from 3076 to 3200, other from 3200 to > 3456MB > > Linus's commit 45fbe3ee01b8e463b28c2751b5dcc0cbdc142d90 in May 2009 added code > to create 'RAM buffer' above top of RAM to ensure that I/O resources do not > start immediately after RAM, but sometime later. Originally it was enforcing > 32MB alignment, now it enforces 64MB. Which means that in VMs with memory size > which is not multiple of 64MB there will be additional 'RAM buffer' resource > present: > > 100000000-1003fffff : System RAM > 100400000-103ffffff : RAM buffer > > When we try to hot-add memory, kernel complains that there was resource > conflict with this fake 'RAM buffer' and hot-added memory is not recognized: > > [ 115.324952] Hotplug Mem Device > [ 115.325549] System RAM resource 100400000 - 10fffffff cannot be added > [ 115.325553] ACPI:memory_hp:add_memory failed > [ 115.326519] ACPI:memory_hp:Error in acpi_memory_enable_device > [ 115.327183] acpi_memhotplug: probe of PNP0C80:00 failed with error -22 > [ 115.327347] > [ 115.327350] driver data not found > [ 115.328808] ACPI:memory_hp:Cannot find driver data > > For now we've modified hotplug code to split hot-added request into smaller > ranges, so only first <= 252MB are unusable, rather than whole xxxGB chunk, but > if 'RAM buffer' could be made dependent on memory hot-plug not available on the > platform, it would be much better. > > Another approach is resurrecting > http://linux.derkeiler.com/Mailing-Lists/Kernel/2008-07/msg06501.html and using > this range instead of all "unclaimed" ranges for placing I/O devices. Then > "RAM buffer" would not be necessary at all. > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>