Re: kdump failed because of hotplug memory adding in kdump kernel

[Vivek Goyal <vgoyal-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On Wed, Jan 08, 2014 at 11:26:43PM +0800, Baoquan wrote:

[..]
> [    1.592222] acpi PNP0A03:03: fail to add MMCONFIG information, can't access extended PCI configuration space under this bridge.
> [    1.605045] PCI host bridge to bus 0000:ff
> [    1.609615] pci_bus 0000:ff: root bus resource [bus ff]
> [    1.632117] System RAM resource [mem 0x01000000-0x7bffffff] cannot be added
> [    1.639892] init_memory_mapping: [mem 0x100000000-0x87fffffff]
> [    1.717793] swapper/0: page allocation failure: order:9, mode:0x84d0
> [    1.724884] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.10.0-59.el7.x86_64 #1
> [    1.732842] Hardware name: QCI QSSC-S4R/QSSC-S4R, BIOS QSSC-S4R.QCI.01.00.S001.032520101647 03/25/2010
> [    1.743224]  0000000000000000 ffff8800339878c8 ffffffff815b64ad ffff880033987950
> [    1.751513]  ffffffff8113a980 ffff88003673ab28 00000000000001fe 0000000000000001
> [    1.759804]  ffff880000000040 ffffffff810bc28a 0000000000000000 0000000000000200
> [    1.768096] Call Trace:                                                                                                                                            [348/1928]
> [    1.770834]  [<ffffffff815b64ad>] dump_stack+0x19/0x1b
> [    1.776561]  [<ffffffff8113a980>] warn_alloc_failed+0xf0/0x160
> [    1.783076]  [<ffffffff810bc28a>] ? on_each_cpu_mask+0x2a/0x60
> [    1.789581]  [<ffffffff8113e92f>] __alloc_pages_nodemask+0x7ff/0xa00
> [    1.796672]  [<ffffffff815ada2c>] vmemmap_alloc_block+0x62/0xba
> [    1.803274]  [<ffffffff815ada99>] vmemmap_alloc_block_buf+0x15/0x3b
> [    1.810263]  [<ffffffff815ab8a6>] vmemmap_populate+0xb4/0x21b
> [    1.816673]  [<ffffffff815adecd>] sparse_mem_map_populate+0x27/0x35
> [    1.823665]  [<ffffffff815ad8bf>] sparse_add_one_section+0x7a/0x185
> [    1.830659]  [<ffffffff8159b74f>] __add_pages+0xaf/0x240
> [    1.836588]  [<ffffffff81047359>] arch_add_memory+0x59/0xd0
> [    1.842804]  [<ffffffff8159ba89>] add_memory+0xb9/0x1b0
> [    1.848638]  [<ffffffff8132dd2c>] acpi_memory_device_add+0x18d/0x26d
> [    1.855728]  [<ffffffff81303b91>] acpi_bus_device_attach+0x7d/0xcd
> [    1.862625]  [<ffffffff8131d92d>] acpi_ns_walk_namespace+0xc8/0x17f
> [    1.869616]  [<ffffffff81303b14>] ? acpi_bus_type_and_status+0x90/0x90
> [    1.876896]  [<ffffffff81303b14>] ? acpi_bus_type_and_status+0x90/0x90
> [    1.884177]  [<ffffffff8131de1c>] acpi_walk_namespace+0x95/0xc5
> [    1.890780]  [<ffffffff81304866>] acpi_bus_scan+0x8b/0x9d
> [    1.896805]  [<ffffffff81a14a15>] acpi_scan_init+0x63/0x160
> [    1.903021]  [<ffffffff81a14830>] acpi_init+0x25d/0x2a6

So basically acpi thinks that some memory block is a hot plug memory
and tries to add it. And that consumes lots of memory and we don't have
that memory in second kernel.

For this reason, we pass a custom E820 map to second kernel so that it
only initializes page tables and memmap array for a very small physical
memory range.

Now question is what is hot plug memory. In this case we have not
physically plugged in any physical memory. So why acpi is considering
this memory to be a hot add memory operation.

Are there memory hotplug slots and these ranges always considered hot added
memory? IOW, what if I hotplug a memory and then reboot the system. Will
new E820 map contain this new memory range or not?

I guess simplest way to solve this problem might be to disable memory hot
plug in kdump kernel. Is there any command line parameter to do that?

If we disable memory hotplug in second kernel, and a hot plug memory
is passed in E820 map, will it still work. Can I access that memory in
second kernel?

Thanks
Vivek