(2014/01/10 16:11), Baoquan wrote:
On 01/09/14 at 02:56pm, Toshi Kani wrote:
On Thu, 2014-01-09 at 16:27 -0500, Vivek Goyal wrote:
On Thu, Jan 09, 2014 at 11:34:30AM -0700, Toshi Kani wrote:
On Thu, 2014-01-09 at 13:23 -0500, Vivek Goyal wrote:
On Thu, Jan 09, 2014 at 10:24:25AM -0700, Toshi Kani wrote:
[..]
I think creating a new command line option is simpler as compared to
creating a new flag in bootparam which in turn disables memory hotplug.
More users can use that option. For example, if for some reason hotplug
code is crashing, one can just disable it on command line as work around
and move on.
I do not have a strong opinion about having such option. However, I
think it is more user friendly to keep the exactmap option works alone
on any platforms.
I think we should create internally a variable which will disable memory
hotplug. And set that variable based on memmap=exactmap, mem=X and also
provide a way to disable memory hotplug directly using command line
option.
Current kexec-tools can use memmap=exactmap and be happy. I am writing
a new kexec syscall and will not be using memmap=exactmap and would need
to use that command line option to disable memory hotplug behavior.
Sounds good to me.
Nobody responded to my other question, so I would ask it again.
Assume we have disabled hotplug memory in second kernel. First kernel
saw hotplug memory and assume crash kernel reserved region came from
there. We will pass this memory in bootparams to second kernel and it
will show up in E820 map. It should still be accessible in second kernel,
is that right?
Yes.
Or there is some dependency on ACPI doing some magic before this memory
range is available in second kernel?
No. The 1st kernel reserves the crash kernel region, which cannot be
hot-deleted. So, this region continues to be accessible by the 2nd
kernel without any operation.
If my understanding is correct:
Now what I understand is if a several memsection is reserved for
crashkernel, then in 2nd kernel, they are just like normal memory.
correct.
In ns
object tree, they are not treated as hotplug memory.
wrong.
They are treated as hotplug memory. But the memory cannot hot removed
because the memory has kernel memory.
Otherwise, any hotplug memory which is not reserved for 2nd kernel can
be parsed and need be added as hotplug memory, and add them into movable
zone.
wrong.
The memory is allocated as normal zone and it is offline.
Am I right?
The other question, e820 reserve is done earlier than acpi
initialization, because acpi_early_init() invocation is very late in
start_kernel(). Does that means at the very beginning all memorys are in
e820, later when acpi_early_init is called, hotplug memory is detected,
they will be moved to different place or need be marked with a specific
flag?
No.
Thanks,
Yasuaki Ishimatsu
I am more curious to know how makedumpfile decides what memory ranges to
dump. The 1st kernel may have performed memory hot-add / delete
operations before a crash, so it needs to know the valid physical
address range at the time of crash, and may not rely on the E820 map
from BIOS (which is stale). Am I right to assume that makedumpfile gets
it from the page tables of the 1st kernel?
makedumpfile just do the dump, what memory ranges to dump is decided in
1st kernel by kexec-tools. In 1st kernel, if kexec-tools executed, it
will find all System Ram memorys which exclude the reserved regions for
kdump kernel, then build a logical elf file, each load segment is one of
these System Ram memory regions, its addr and length is written into the
program header.
Then makedumpfile just read this elf file, and read all of them and
dump.
If after kexec-tools execution and before crash, a hotplug memory is
removed, udev will check this and trigger a kdump restart, kexec-tools
is executed again, System Ram region information are stored. The logical
file header will be passed to 2nd kernel.
Thanks,
-Toshi
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