Re: makedumpfile memory usage grows with system memory size

From: Don Zickus <dzickus@redhat.com>
To: Ken'ichi Ohmichi <oomichi@mxs.nes.nec.co.jp>
Cc: kexec@lists.infradead.org
Subject: Re: makedumpfile memory usage grows with system memory size
Date: Thu, 29 Mar 2012 09:05:14 -0400	[thread overview]
Message-ID: <20120329130514.GK18218@redhat.com> (raw)
In-Reply-To: <20120329170918.4223e816.oomichi@mxs.nes.nec.co.jp>

Hi Ken'ichi-san,

On Thu, Mar 29, 2012 at 05:09:18PM +0900, Ken'ichi Ohmichi wrote:
> 
> Hi Don-san,
> 
> On Wed, 28 Mar 2012 17:22:04 -0400
> Don Zickus <dzickus@redhat.com> wrote:
> > 
> > I was talking to Vivek about kdump memory requirements and he mentioned
> > that they vary based on how much system memory is used.
> > 
> > I was interested in knowing why that was and again he mentioned that
> > makedumpfile needed lots of memory if it was running on a large machine
> > (for example 1TB of system memory).
> > 
> > Looking through the makedumpfile README and using what Vivek remembered of
> > makedumpfile, we gathered that as the number of pages grows, the more
> > makedumpfile has to temporarily store the information in memory.  The
> > possible reason was to calculate the size of the file before it was copied
> > to its final destination?
> 
> makedumpfile uses the system memory of 2nd-kernel for a bitmap if RHEL.
> The bitmap represents each page of 1st-kernel is excluded or not.
> So the bitmap size depends on 1st-kernel's system memory.
> 
> makedumpfile creates a file /tmp/kdump_bitmapXXXXXX as the bitmap,
> and the file is created on 2nd-kernel's memory if RHEL, because
> RHEL does not mount a root filesystem when 2nd-kernel is running.

Ok.

> 
> 
> > I was curious if that was true and if it was, would it be possible to only
> > process memory in chunks instead of all at once.
> > 
> > The idea is that a machine with 4Gigs of memory should consume the same
> > the amount of kdump runtime memory as a 1TB memory system.
> > 
> > Just trying to research ways to keep the memory requirements consistent
> > across all memory ranges.
> 
> I think the above purpose is good, and I don't have any idea for reducing
> the bitmap size. And now I am out of makedumpfile development.
> Kumagai-san is the makedumpfile maintainer now, and he will help you.

Thanks for the feedback, I'll wait for Kumagai-san's response then.

Cheers,
Don

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