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    SubjectRe: [Patch 6/8] powerpc: add CONFIG_KEXEC_AUTO_RESERVE
    On Tue, Aug 25, 2009 at 02:23:04PM +0800, Amerigo Wang wrote:
    > Michael Ellerman wrote:
    >> On Fri, 2009-08-21 at 02:55 -0400, Amerigo Wang wrote:
    >>> Introduce a new config option KEXEC_AUTO_RESERVE for powerpc.
    >>> Index: linux-2.6/arch/powerpc/Kconfig
    >>> ===================================================================
    >>> --- linux-2.6.orig/arch/powerpc/Kconfig
    >>> +++ linux-2.6/arch/powerpc/Kconfig
    >>> @@ -346,6 +346,17 @@ config KEXEC
    >>> support. As of this writing the exact hardware interface is
    >>> strongly in flux, so no good recommendation can be made.
    >>> +config KEXEC_AUTO_RESERVE
    >>> + bool "automatically reserve memory for kexec kernel"
    >>> + depends on KEXEC
    >>> + default y
    >>> + ---help---
    >>> + Automatically reserve memory for a kexec kernel, so that you don't
    >>> + need to specify numbers for the "crashkernel=X@Y" boot option,
    >>> + instead you can use "crashkernel=auto". To make this work, you need
    >>> + to have more than 4G memory. On PPC, 256M is reserved, 1/32 memory
    >>> + on PPC64, but it will not exceed 1T/32.
    >> To be honest I don't see why this logic goes in the kernel. It seems to
    >> me that it's policy how much memory you devote to the crash kernel vs
    >> the production kernel. It depends on what kind of crash kernel you're
    >> loading, a minimal UP dump kernel, or a full-featured SMP behemoth, An
    >> it depends on how much memory you're willing to leave idle in the
    >> off-chance you crash.
    > True, but since in the crash kernel, we have very little memory, so
    > probably loading a full-featured SMP kernel doesn't make much sense...
    > And in patch 1/8, I introduced a way to free the reserved memory at
    > run-time.
    >> That aside, I don't see how this will be useful in practice, if it only
    >> works for memory sizes over 4G? Or are we saying that people with less
    >> than 4G don't need crash kernels? If we're not saying that, those users,
    >> or those users' distros, still need to do some logic to work out if they
    >> have < 4GB of memory and if so pick a crash kernel size. So why can't
    >> they pick the size in the > 4GB case also?
    > No, we set 4G as a threshold because we only want this work when have
    > have enough memory which is defined as 4G currently... This can be
    > changed to arch-dependent, e.g. ppc. I am very open to this.

    So the distro/admin have to use crashkernel=auto for machines having more
    than 4GB RAM and for machines with less than 4GB RAM they have to use the
    crashkernel=x@y (or extended crashkernel syntax)? IMHO it will be nice if
    crashkernel=auto could handle all of the situations.

    M. Mohan Kumar

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      Last update: 2009-08-25 12:31    [W:0.027 / U:67.976 seconds]
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