Reducing the size of the dump file/speeding up collection

[Nikolay Borisov]

Yeah, I did see the commit browser. But in my case I haven't even tested
the split option so I guess there are things to try. Am I correct in my
understanding as to how --split is supposed to work ( i tried that to no
avail though):

My core_collector line is this:

core_collector makedumpfile --message-level 1 -d 3 --split dump1 dump2
dump3 dump4 dump5 dump6

And then in /etc/sysconfig/kdump I have:

KDUMP_COMMANDLINE_APPEND="irqpoll nr_cpus=6 reset_devices
cgroup_disable=memory mce=off"

(the machine I'm testing on has 4 cores x2 hyperthreads so 8 logical
cores in total). Do I need to do something else to utilize the --split
option?

On 09/18/2015 05:38 AM, qiaonuohan wrote:
> On 09/17/2015 02:32 PM, Nikolay Borisov wrote:
>> Hi Qiao,
>>
>> Thanks for the reply. So far I haven't been using the the compression
>> feature of makedumpfile. But I want to ask if anything wouldn't
>> compression make the dump process slower since in addition to having to
>> write the dump to disk it also has to compress it which would put more
>> strain on the cpu. Also, which part of the dump process is the
>> bottleneck:
>>
>> - Reading from /proc/vmcore - that has mmap support so should be fairly
>> fast?
>> - Discarding unnecessary pages as memory is being scanned?
>> - Writing/compressing content to disk?
> 
> I cannot recall percentage of each part. But writing/compression takes most
> of the time
> 
> 1. mmap is used for reading faster
> 2. --split is used to split the dump task into several processes, so
> compressing
>    and writing will be speeded up.
> 3. multiple-thread is another option for speeding up compressing, it is
> a recently
>    committed patch, so you cannot find it in the master branch, checkout
> devel branch
>    or find it here:
> 
> http://sourceforge.net/p/makedumpfile/code/commit_browser
> 
> Make makedumpfile available to read and compress pages parallelly.
> 
>>
>> Regards,
>> Nikolay
>>
>> On 09/17/2015 06:27 AM, qiaonuohan wrote:
>>> On 09/16/2015 04:30 PM, Nikolay Borisov wrote:
>>>> Hello,
>>>>
>>>> I've been using makedumpfile as the crash collector with the -d31
>>>> parameter. The machine this is being run on usually have 128-256GB of
>>>> ram and the resulting crash dumps are in the range of 14-20gb which is
>>>> very bug for the type of analysis I'm usually performing on crashed
>>>> machine. I was wondering whether there is a way  to further reduce the
>>>> size and the time to take the dump (now it takes around 25 minutes to
>>>> collect such a dump). I've seen reports where people with TBs of ram
>>>> take that long, meaning for a machine with 256gb it should be even
>>>> faster. I've been running this configuration on kernels 3.12.28 and 4.1
>>>> where mmap for the vmcore file is supported.
>>>>
>>>> Please advise
>>>
>>> Hi nikolay,
>>>
>>> Yes, this issue is what we are concerning a lot.
>>> About the current situation, try --split, it will save time.
>>>
>>>
>>> And lzo/snappy instead of zlib, these two compression format are faster
>>> but need more space to save. Or if you still want zlib (to save space),
>>> try multiple threads, check the following site, it will help you:
>>>
>>> https://lists.fedoraproject.org/pipermail/kexec/2015-September/002322.html
>>>
>>>
>>>
>> .
>>
> 
>