Re: Linux Kernel Dump Summit 2005

[OBATA Noboru <noboru.obata.ar@hitachi.com>]

On Wed, 19 Oct 2005, Takao Indoh wrote:
> > 
> > Could you briefly explain the implementation of partial dump in
> > diskdump for those who are not familiar with it?
> > 
> > - Levels of partial dump (supported page categories)
> > - How to indentify the category (kernel data structure used)
> 
> Ok.
> Partial dump of diskdump defines 5 filters.
> 
> #define DUMP_EXCLUDE_CACHE 0x00000001 /* Exclude LRU & SwapCache pages*/
> #define DUMP_EXCLUDE_CLEAN 0x00000002 /* Exclude all-zero pages */
> #define DUMP_EXCLUDE_FREE  0x00000004 /* Exclude free pages */
> #define DUMP_EXCLUDE_ANON  0x00000008 /* Exclude Anon pages */
> #define DUMP_SAVE_PRIVATE  0x00000010 /* Save private pages */

> DUMP_EXCLUDE_FREE has some risks. If this filter is enable, diskdump
> scans free page linked lists. If the list is corrupt, diskdump may hang.
> Therefore, I always use level-19 (EXCLUDE_CACHE & EXCLUDE_CLEAN &
> SAVE_PRIVATE).
> 
> DUMP_EXCLUDE_CACHE reduces dump size effectively when file caches on
> memory are big. I don't use DUMP_EXCLUDE_ANON because user data(user
> stack, thread stack, mutex, etc.) is sometimes needed to investigate
> dump.
> DUMP_SAVE_PRIVATE is needed for filesystem. Filesystem (journal) uses
> PG_private pages, so these pages is necessary to investigate
> trouble of filesystem. 

Thank you for filters' description as well as the recommended
filter combination.

I'm just wondering the use of DUMP_EXCLUDE_CLEAN.  When a zero
page is excluded from a dump, how people know?  What I'm afraid
is that people would see an error (e.g., no such page in a dump)
in analyzing such a dump and be confused why.  Because it is a
cache, or zero-cleared, or, ...?  Any ideas?

Regards,

-- 
OBATA Noboru (noboru.obata.ar@hitachi.com)