On Tue, 4 Jan 2011 13:51:48 -0800 Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > > (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. > > Hmm ? Why do you need to place "hot-added" memory's address range next to System RAM ? Sparsemem allows sparse memory layout. Is it very difficult ? Thanks, -Kame -- 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>