[Crash-utility] what is recommended dump level (makedumpfile)

[Dave Anderson]

----- "Tokuhisa Inagaki" <tokuhisa.inagaki at ctc-g.co.jp> wrote:

> Hi, all.
> 
> what is recommended dump level when using makedumpfile
> (kdump)? I'm looking for explanation like this.
> 
> ------------ from diskdump document --------------------
> Note that the partial dump feature has some risks.  There
> are memory management lists which are scanned for a page's
> memory attribute, so if the list has been corrupted, the
> scanning process may fail.  For example, when specifying a
> dump_level from 4-7 or from 12-15, the kernel's free page
> linked lists are scanned; if the list is corrupt, diskdump
> may hang.  Furthermore, it is possible that a page type
> that has been skipped may be necessary to fully investigate
> the cause of some issues.  Therefore, a memory collection
> level should be selected to suit each situation.  The
> recommended level is 19, because it is easiest to determine
> whether a page is zero-filled or if it is a page cache page,
> and because no page lists need to be traversed.
> -------------------------------------------------------
> 
> Does anyone know document describing these things
> when using makedumpfile ?
> 
> 
> Thanks,
> toku.

I don't know of any document for makedumpfile other than the
/usr/share/doc/kexec-tools-<version>/kexec-kdump-howto.txt
and the output of "makedumpfile -h".  Neither of those has
any caveats such as the diskdump document above, but I'm
guessing that the same kind of issues would apply when makedumpfile
walks page lists, the mem_map, etc.  But I don't know what the
failure mode would be, given that it's a user application as opposed
to a kernel module.

In any case, the makedumpfile maintainers are on this list
and hopefully can shed some light on your query.

Dave