[PATCH] kexec-kdump-howto: add the debugging tip for rd.kodebug

[Xunlei Pang]

Update the doc to include the help for rd.kodebug.

Signed-off-by: Xunlei Pang <xlpang(a)redhat.com&gt;
---
 kexec-kdump-howto.txt | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/kexec-kdump-howto.txt b/kexec-kdump-howto.txt
index f46563f..87f3821 100644
--- a/kexec-kdump-howto.txt
+++ b/kexec-kdump-howto.txt
@@ -706,4 +706,41 @@ Debugging Tips
 
   Now minicom should be logging serial console in file console-logs.
 
+- Debug the large memory consumption by kernel modules
+
+  Besides dracut "rd.memdebug=[0-3]" support to debug kdump system memory,
+  kdump supports a fine-grained memory monitor for kernel modules to help
+  figure out which kernel module consumes a large amount of memory(the larger,
+  the more precise the result is).
+
+  One can pass "rd.kodebug" to kdump kernel through
"KDUMP_COMMANDLINE_APPEND"
+  defined in /etc/sysconfig/kdump, touch /etc/kdump.conf, restart kdump, then
+  the memory consumption information by kernel modules will be printed out to
+  the console before the vmcore dumping starts.
+
+  As an example, it prints out something below:
+  == debug_mem for kernel modules during loading begin ==
+  0 pages consumed by "pata_acpi" [load finished]
+  0 pages consumed by "ata_generic" [load finished]
+  0 pages consumed by "drm" [load finished]
+  1 pages consumed by "ttm" [load finished]
+  0 pages consumed by "drm_kms_helper" [load finished]
+  834 pages consumed by "qxl" [load finished]
+  0 pages consumed by "mii" [load finished]
+  5 pages consumed by "8139cp" [load finished]
+  0 pages consumed by "8139too" [load finished]
+  0 pages consumed by "virtio" [load finished]
+  0 pages consumed by "virtio_ring" [load finished]
+  10 pages consumed by "virtio_pci" [load finished]
+  0 pages consumed by "serio_raw" [load finished]
+  0 pages consumed by "crc32c_intel" [load finished]
+  199 pages consumed by "virtio_console" [load finished]
+  0 pages consumed by "libcrc32c" [load finished]
+  8 pages consumed by "xfs" [load finished]
+  == debug_mem for kernel modules during loading end ==
+
+  If you encounters OOM when using the feature, you can enlarge the reserved memory
+  via "crashkernel" and try again. If you find some kernel module is not
included
+  in the print, you can enlarge the trace buffer via "trace_buf_size"(the
default
+  size set is 5MB in total for all cpus), and try again.
 
-- 
1.8.3.1