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kexec-kdump-howto.txt: Add notes about device dump

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Currently there are two issues with device dump:
  - It may use too much memory
  - kdump won't automatically include required driver in second kernel

User should manually reserve enough memory, and include the required
driver by using extra_modules. Add some notes about the issues in
kexec-kdump-howto.txt

Signed-off-by: Kairui Song <kasong@redhat.com>
Acked-by: Dave Young <dyoung@redhat.com>
This commit is contained in:
Kairui Song 2019-05-29 17:00:43 +08:00
parent ff329689b3
commit 3e8526cf04
1 changed files with 17 additions and 0 deletions
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17
kexec-kdump-howto.txt
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@ -698,6 +698,23 @@ crash kernel according, or update your encryption setup.
It's recommanded to use a non-encrypted target (eg. remote target)
instead.
Notes on device dump:
Device dump allows drivers to append dump data to vmcore, so you can
collect driver specified debug info. The drivers could append the
data without any limit, and the data is stored in memory, this may
bring a significant memory stress. So device dump is disabled by default
by passing "novmcoredd" command line option to the kdump capture kernel.
If you want to collect debug data with device dump, you need to modify
"KDUMP_COMMANDLINE_APPEND=" value in /etc/sysconfig/kdump and remove the
"novmcoredd" option. You also need to increase the "crashkernel=" value
accordingly in case of OOM issue.
Besides, kdump initramfs won't automatically include the device drivers
which support device dump, only device drivers that are required for
the dump target setup will be included. To ensure the device dump data
will be included in the vmcore, you need to force include related
device drivers by using "extra_modules" option in /etc/kdump.conf
Parallel Dumping Operation
==========================
Kexec allows kdump using multiple cpus. So parallel feature can accelerate