On Fri, Nov 15, 2013 at 02:24:25PM -0800, Yinghai Lu wrote:
> On Fri, Nov 15, 2013 at 10:03 AM, Vivek Goyal <vgo...@redhat.com> wrote:
> > On Fri, Nov 15, 2013 at 09:33:41AM -0800, Yinghai Lu wrote:
>
> >> I have one system with 6TiB memory, kdump does not work even
> >> crashkernel=512M in legacy mode. ( it only work on system with
> >> 4.5TiB).
> >
> > Recently I tested one system with 6TB of memory and dumped successfully
> > with 512MB reserved under 896MB. Also I have heard reports of successful
> > dump of 12TB system with 512MB reserved below 896MB (due to cyclic
> > mode of makedumpfile).
> >
> > So with newer releases only reason one might want to reserve more
> > memory is that it might provide speed benefits. We need more testing
> > to quantify this.
>
> You may need bunch of PCIe cards installed.
>
> The system with 6TiB + 16 PCIe cards, second kernel OOM.
> The system with 4.5TiB + 16 PCIe cards, second kernel works with vmcore
> dumped.
Yinghai,
Your original email said you were using "legacy mode". Does this mean
you're not running makedumpfile in cyclic mode? Cyclic mode makes
a *big* difference in memory foot print of makedumpfile.
thanks
Jerry
>
> >
> >> --- first kernel can reserve the 512M under 896M, second kernel will
> >> OOM as it load driver for every pci devices...
> >>
> >> So why would RH guys not spend some time on optimizing your kdump initrd
> >> build scripts and only put dump device related driver in it?
> >
> > Try latest Fedora and that's what we do. Now we have moved to dracut
> > based initramfs generation and we tell dracut that build initramfs for
> > host and additional dump destination and dracut builds it for those only.
> > I think there might be scope for further optimization, but I don't think
> > that's the problem any more.
>
> Good. Assume that will be in RHEL 7.
>
> >
> > So issue remains that crashkernel=X,high is not a good default choice
> > because it consumes extra 72M which we don't have to.
>
> then if it falls into 896~4G, user may still need to update kexec-tools ?
>
> Thanks
>
> Yinghai
--
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Jerry Hoemann Software Engineer Hewlett-Packard
3404 E Harmony Rd. MS 57 phone: (970) 898-1022
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email: jerry.hoem...@hp.com
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