mm, memory_hotplug: improve memory offlining failures debugging

Hi,
this has been posted as an RFC [1]. I have screwed during rebasing so there were few compilation issues in the previous version. I have also integrated review feedback from Andrew and Anshuman.

I have been promissing to improve memory offlining failures debugging for quite some time. As things stand now we get only very limited information in the kernel log when the offlining fails. It is usually only

[ 1984.506184] rac1 kernel: memory offlining [mem 0x82600000000-0x8267fffffff] failed

without no further details. We do not know what exactly fails and for what reason. Whenever I was forced to debug such a failure I've always had to do a debugging patch to tell me more. We can enable some tracepoints but it would be much better to get a better picture without using them.

This patch series does 2 things. The first one is to make dump_page more usable by printing more information about the mapping patch 1. Then it reduces the log level from emerg to warning so that this function is usable from less critical context patch 2. Then I have added more detailed information about the offlining failure patch 4 and finally add dump_page to isolation and offlining migration paths. Patch 3 is a trivial cleanup.

Does this look go to you?

[1] http://lkml.kernel.org/r/[email protected]

Shortlog
Michal Hocko (5):
mm: print more information about mapping in __dump_page
mm: lower the printk loglevel for __dump_page messages
mm, memory_hotplug: drop pointless block alignment checks from __offline_pages mm, memory_hotplug: print reason for the offlining failure
mm, memory_hotplug: be more verbose for memory offline failures

Diffstat

 mm/debug.c          | 23 ++++++++++++++++++-----
 mm/memory_hotplug.c | 52 +++++++++++++++++++++++++++++++---------------------
 mm/page_alloc.c     |  1 +
 3 files changed, 50 insertions(+), 26 deletions(-)