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

[Tokuhisa Inagaki]

Thanks Ken'ichi, Dave!

> As Dave said, makedumpfile has the same risk as the partial dump
> feature of diskdump. If excluding free pages and free pages linked
> lists are corrupt, makedumpfile fails. So I recommend dump_level 15
> (excluding zero pages, cache pages, user data pages. not excluding
> free pages) because of the same reason as diskdump.

Thank you for helpful advice.
I will refer to your information.

> FYI:
> If using RHEL5.2 or older, it is better that you update it to RHEL5.3.

OK.
Latest makedumpfile will be used in the future.

Thanks,
Toku.


Ken'ichi Ohmichi wrote:
> Hi,
> 
> Dave Anderson wrote:
>>> 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.
> 
> As Dave said, makedumpfile has the same risk as the partial dump
> feature of diskdump. If excluding free pages and free pages linked
> lists are corrupt, makedumpfile fails. So I recommend dump_level 15
> (excluding zero pages, cache pages, user data pages. not excluding
> free pages) because of the same reason as diskdump.
> 
> 
> FYI:
> If using RHEL5.2 or older, it is better that you update it to RHEL5.3.
> 
> RHEL5.2's makedumpfile has a buffer-handling bug and it cannot exclude
> right page occasionally. This bug has been fixed on RHEL5.3, so if using
> RHEL5.2 or older you should update it.
> 
> This bug has been fixed on makedumpfile version 1.3.0, and The following
> thread is about this bug:
> http://lists.infradead.org/pipermail/kexec/2008-September/002629.html
> 
> 
> Thanks
> Ken'ichi Ohmichi
> 
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