Re: [RFC][PATCH] Add --split support for dump on filesystem

[HATAYAMA Daisuke]

Sorry for delayed response.

From: Vivek Goyal 
Subject: Re: [RFC][PATCH] Add --split support for dump on filesystem
Date: Mon, 31 Mar 2014 08:47:12 -0400
> On Mon, Mar 31, 2014 at 07:21:20PM +0900, HATAYAMA Daisuke wrote:
>
> [..]
> > Yes, I also think the design needs to be changed for multiple
> > disks...
> > So I'm not thinking optimistically you reacts positive
> > attitude to the feature..
>
> I am not sure what does this mean?
>
> [..]
> > > > Anyway, benchmark will be needed to discuss this topic in detail.
> > >
> > > Agreed. First we need to implement that new mode and see if it gives
> > > us good performance or not.
> >
> > I've already investigated the feature in processing level but I need
> > some more time to make a patch set because supporting pthread need to
> > change makedumpfile to a certain amount. Please wait for now.
>
> Sure not a problem. No rush. I was just brain storming to figure out
> what features are already present and what new features are required. So
> atleast we agree that dumping to single file while having multiple threads
> for filtering and compression is a new feature.
>
> Till we get that feature, I guess customers can achieve that parallelism
> by dumping to multiple files (to same adaptor) and then reassembling
> those files manually later.
>
> Thanks
> Vivek

So, I'll post a patch to support --split patch as a means of
supporting parallelism. Do you agree with this direction?

In the patch, --split is no logner automatically inserted. User should
specify it in core_collector explicitly, and then kdump script detects
it and appends a multiple vmcore argumetns accordingly. The number of
the multiple arguments is the number of cpus running in the 2nd
kernel, i.e., the number specified in nr_cpus.

That is, if in /etc/kdump.conf core_collector is specified as

core_collector makedumpfile --split -l -d 31

and the number of online cpus on the 2nd kernel is more than 2, say 3
here, then, the following command is executed:

$ makedumpfile --split -l -d 31 /proc/vmcore vmcore-0-incomplete vmcore-1-incomplete vmcore-2-incomplete

If makedumpfile --split is specified but the number of online cpus on
the 2nd kernel is 1, then --split is removed as makedumpfile fails
while warning that more vmcore arugments are needed.

I'll post a patch for how-to file to document this properly.

Thanks.
HATAYAMA, Daisuke