Messages in this thread | | | Date | Tue, 25 Aug 2009 14:23:04 +0800 | From | Amerigo Wang <> | Subject | Re: [Patch 6/8] powerpc: add CONFIG_KEXEC_AUTO_RESERVE |
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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.
> Also the numbers seem a bit arbitrary. 4GB ? 256M ? 1/32? I don't think > we really want to be blowing 32GB on a crash kernel, even if we do have > 1T of RAM :) >
Ah, maybe, to be honest, I am not familiar with ppc at all.
Please feel free to suggest other numbers for ppc (or other algorithms to reserve memory automatically for ppc).
Thanks!
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