[RFC PATCH 0/4] makedumpfile: cyclic processing to keep memory consumption.

[Atsushi Kumagai]

Hello,

I made the prototype of cyclic processing to keep memory consumption.
I attache the patch set based on v1.4.4, I would like to get your advice.

Introduction:

 - The basic idea of cyclic processing is represented as below.
 - cyclic processing doesn't use temporary bitmap file, store partial bitmap data
   in memory only for each cycle instead.
 - The prototype only support compressed kdump format.
 - The prototype worked for almost kernel version except some kernel disabled PAE 
   in my environment.

Basic idea (HATAYAMA-san wrote):

   +------------------------------------------+
   |    main header (struct disk_dump_header) |
   |------------------------------------------+
   |    sub header (struct kdump_sub_header)  |
   |------------------------------------------+
   |                                          | <-- 1st cycle
   | -  -  -  -  -  -  -  -  -  -  -  -  -  - |
   |            1st-bitmap                    | <-- 2nd cycle
   | -  -  -  -  -  -  -  -  -  -  -  -  -  - |
   |                                          | <-- 3rd cycle
   |------------------------------------------+
   |                                          | <-- 1st cycle
   | -  -  -  -  -  -  -  -  -  -  -  -  -  - |
   |            2nd-bitmap                    | <-- 2nd cycle
   | -  -  -  -  -  -  -  -  -  -  -  -  -  - |
   |                                          | <-- 3rd cycle
   |------------------------------------------+
   |                                          | <-- 1st cycle
   | -  -  -  -  -  -  -  -  -  -  -  -  -  - |
   |            page header                   | <-- 2nd cycle
   | -  -  -  -  -  -  -  -  -  -  -  -  -  - |
   |                                          | <-- 3rd cycle
   |------------------------------------------|
   |                                          |
   |            page data                     | <-- 1st cycle
   |                                          |
   | -  -  -  -  -  -  -  -  -  -  -  -  -  - |
   |            page data                     | <-- 2nd cycle
   | -  -  -  -  -  -  -  -  -  -  -  -  -  - |
   |                                          |
   |                                          |
   |            page data                     | <-- 3rd cycle
   |                                          |
   |                                          |
   +------------------------------------------+


How to use:
  
  Specify 'K' option, then makedumpfile works cyclically.

Example:

  a. normal processing:

    $ makedumpfile -cd31 vmcore testdump.cd31
    Copying data                       : [100 %]

    The dumpfile is saved to testdump.cd31.

    makedumpfile Completed.

  b. cyclic processing (too many messages will be displayed):

    $ makedumpfile -Kcd31 vmcore testdump.Kcd31
    Copying data                       : [  5 %]
    Excluding free pages               : [100 %]
    ...
    Excluding free pages               : [100 %]
    Copying data                       : [100 %]

    The dumpfile is saved to testdump.Kcd31.

    makedumpfile Completed.

  c. compare each dumpfiles:

    $ cmp testdump.cd31 testdump.Kcd31
    $

TODO:

 - Optimize code for performance.
   (e.g. initialize for compression is done every cycle, it's a waste.)
 - Support ELF format.
 - Consider suitable size of target region.
 - Fix some messages.
 - And something noticed by you.


Thanks
Atsushi Kumagai