[PATCH] Makedumpfile: vmcore size estimate

Baoquan He bhe at redhat.com
Mon Jun 23 06:05:33 PDT 2014

On 06/23/14 at 08:36am, Vivek Goyal wrote:
> On Wed, Jun 11, 2014 at 08:39:05PM +0800, Baoquan He wrote:
> > sudo makedumpfile -E -d 31 --vmcore-estimate /proc/kcore /var/crash/kcore-dump
> > 
> > Questions:
> > 1. Or we can get the dumpable page numbers only, then calculate the estimated
> > vmcore size by a predifined factor if it's kdump compressed dumping. E.g if
> > lzo dump, we assume the compression ratio is 45%, then the estimate size is
> > equal to: (dumpable page numbers) * 4096* 45%.
> I think that we can probably not guess the saving from compression.
> Compression ratio varies based on content of page. So if we keep it simple
> and just calculate the number of pages which will be dumped and multiply
> it by page size, that number will be much more accurate (for current
> system).

Yeah, this is another plan. Then the output will be the size of elf
dump. If user configured the kdump compression, such as lzo/snappy, they
can just estimate it by themselves. It's OK if user can accept this
since this is much more accurate.

Hi Anders,

Do you have any comments on this? I found you are concerned with this
issue too.


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