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    SubjectRe: [PATCH 0/3] Early use of boot service memory
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    On Fri, Nov 15, 2013 at 10:03 AM, Vivek Goyal <vgoyal@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.

    >
    >> --- 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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