Re: [PATCH] Reserve memory for kdump kernel within RMO region
On 11/27/2009 12:56 AM, Bernhard Walle wrote: M. Mohan Kumar schrieb: On 11/26/2009 12:22 AM, Bernhard Walle wrote: M. Mohan Kumar schrieb: Reserve memory for kdump kernel within RMO region When the kernel size exceeds 32MB(observed with some distros), memory for kdump kernel can not be reserved as kdump kernel base is assumed to be 32MB always. When the kernel has CONFIG_RELOCATABLE option enabled, provide the feature to reserve the memory for kdump kernel anywhere in the RMO region. Hi Bernhard, Correct me if I'm wrong, but: CONFIG_RELOCATABLE is for the kernel that gets loaded as crashkernel, not for the kernel that loads the crashkernel. So it would be perfectly fine that a kernel that has not CONFIG_RELOCATABLE set would load another kernel that has CONFIG_RELOCATABLE set on an address != 32 M. No, with relocatable option, the same kernel is used as both production and kdump kernel. Can be, but it's not strictly necessary. It depends what userland does. Especially it's possible that a non-relocatable, self-compiled kernel loads a relocatable distribution kernel as capture kernel. I don't understand why a non-relocatable kernel will use relocatable kernel for capturing kdump kernel. The idea for relocatable kernel is to avoid using two different kernels to capture kernel dump. Also, it would make sense to make the behaviour symmetric across platforms. Currently we have: - x86 and ia64: Without offset on command line, use any offset With offset on command line, use that offset and fail if no memory is available at that offset. - ppc64: Always use 32M and ignore the offset. If your patch gets applied, we have: - ppc64: With CONFIG_RELOCATABLE, use any offset With offset on command I don't see why the behaviour on ppc64 should be completely different. Having maintained kdump for SUSE for x86, ia64 and partly ppc64 in the past, I always felt that ppc64 is more different from x86 than ia64 is from x86. That's one more step into that direction without a technical reason. Also with the crashkernel=auto parameter (patches are not yet merged), the crashkernel base (offset) by default would be 32MB. In this case if a kernel passed with crashkernel=auto and if the first kernel size exceeds 32MB, memory for kdump kernel will always fail. Having that all said: If your patch gets in mainline kernel, than we should change the behaviour also for x86 and ia64. Regards, Bernhard ___ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec
Re: [PATCH] Reserve memory for kdump kernel within RMO region
On Fri, Nov 27, 2009 at 02:05:46PM +0530, M. Mohan Kumar wrote: On 11/27/2009 12:56 AM, Bernhard Walle wrote: M. Mohan Kumar schrieb: On 11/26/2009 12:22 AM, Bernhard Walle wrote: M. Mohan Kumar schrieb: Reserve memory for kdump kernel within RMO region When the kernel size exceeds 32MB(observed with some distros), memory for kdump kernel can not be reserved as kdump kernel base is assumed to be 32MB always. When the kernel has CONFIG_RELOCATABLE option enabled, provide the feature to reserve the memory for kdump kernel anywhere in the RMO region. Hi Bernhard, Correct me if I'm wrong, but: CONFIG_RELOCATABLE is for the kernel that gets loaded as crashkernel, not for the kernel that loads the crashkernel. So it would be perfectly fine that a kernel that has not CONFIG_RELOCATABLE set would load another kernel that has CONFIG_RELOCATABLE set on an address != 32 M. No, with relocatable option, the same kernel is used as both production and kdump kernel. Can be, but it's not strictly necessary. It depends what userland does. Especially it's possible that a non-relocatable, self-compiled kernel loads a relocatable distribution kernel as capture kernel. I don't understand why a non-relocatable kernel will use relocatable kernel for capturing kdump kernel. The idea for relocatable kernel is to avoid using two different kernels to capture kernel dump. True, but that doesn't necessarily mean that using a relocatable kdump kernel is required. Well, hopefully not. Also, it would make sense to make the behaviour symmetric across platforms. Currently we have: - x86 and ia64: Without offset on command line, use any offset With offset on command line, use that offset and fail if no memory is available at that offset. - ppc64: Always use 32M and ignore the offset. If your patch gets applied, we have: - ppc64: With CONFIG_RELOCATABLE, use any offset With offset on command I don't see why the behaviour on ppc64 should be completely different. Having maintained kdump for SUSE for x86, ia64 and partly ppc64 in the past, I always felt that ppc64 is more different from x86 than ia64 is from x86. That's one more step into that direction without a technical reason. Also with the crashkernel=auto parameter (patches are not yet merged), the crashkernel base (offset) by default would be 32MB. In this case if a kernel passed with crashkernel=auto and if the first kernel size exceeds 32MB, memory for kdump kernel will always fail. Having that all said: If your patch gets in mainline kernel, than we should change the behaviour also for x86 and ia64. Regards, Bernhard ___ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec ___ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec
Re: [PATCH] Reserve memory for kdump kernel within RMO region
Hi, As of now the kdump kernel base is fixed to be 32MB. The intention of this patch is to modify that behaviour (for relocatable kernels) * Regular kernel size may exceed 32MB, in this case we can't have kdump kernelbase as 32MB. * crashkernel=auto also assumes that kdump kernelbase as 32MB, and it may also fail in reserving memory for kdump kernel. On 11/27/2009 12:56 AM, Bernhard Walle wrote: M. Mohan Kumar schrieb: On 11/26/2009 12:22 AM, Bernhard Walle wrote: M. Mohan Kumar schrieb: Reserve memory for kdump kernel within RMO region When the kernel size exceeds 32MB(observed with some distros), memory for kdump kernel can not be reserved as kdump kernel base is assumed to be 32MB always. When the kernel has CONFIG_RELOCATABLE option enabled, provide the feature to reserve the memory for kdump kernel anywhere in the RMO region. Hi Bernhard, Correct me if I'm wrong, but: CONFIG_RELOCATABLE is for the kernel that gets loaded as crashkernel, not for the kernel that loads the crashkernel. So it would be perfectly fine that a kernel that has not CONFIG_RELOCATABLE set would load another kernel that has CONFIG_RELOCATABLE set on an address != 32 M. No, with relocatable option, the same kernel is used as both production and kdump kernel. Can be, but it's not strictly necessary. It depends what userland does. Especially it's possible that a non-relocatable, self-compiled kernel loads a relocatable distribution kernel as capture kernel. Also, it would make sense to make the behaviour symmetric across platforms. Currently we have: - x86 and ia64: Without offset on command line, use any offset With offset on command line, use that offset and fail if no memory is available at that offset. - ppc64: Always use 32M and ignore the offset. If your patch gets applied, we have: - ppc64: With CONFIG_RELOCATABLE, use any offset With offset on command I don't see why the behaviour on ppc64 should be completely different. Having maintained kdump for SUSE for x86, ia64 and partly ppc64 in the past, I always felt that ppc64 is more different from x86 than ia64 is from x86. That's one more step into that direction without a technical reason. Having that all said: If your patch gets in mainline kernel, than we should change the behaviour also for x86 and ia64. Regards, Bernhard ___ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec ___ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec
Re: [PATCH] Reserve memory for kdump kernel within RMO region
M. Mohan Kumar schrieb: Hi, As of now the kdump kernel base is fixed to be 32MB. The intention of this patch is to modify that behaviour (for relocatable kernels) * Regular kernel size may exceed 32MB, in this case we can't have kdump kernelbase as 32MB. * crashkernel=auto also assumes that kdump kernelbase as 32MB, and it may also fail in reserving memory for kdump kernel. I'm not opposed to remove the 32MB restriction, but I would like to make the behaviour independent of CONFIG_RELOCATABLE like it's on x86: - Use 32M if one specifies x...@32m - Use preferrably 32M, but fall back to another address if one specifies xxx or x...@0m. I don't see any problem with that. But it would make behaviour equal accross platforms. Regards, Bernhard ___ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec
Re: [PATCH] Reserve memory for kdump kernel within RMO region
M. Mohan Kumar schrieb: On 11/26/2009 12:22 AM, Bernhard Walle wrote: M. Mohan Kumar schrieb: Reserve memory for kdump kernel within RMO region When the kernel size exceeds 32MB(observed with some distros), memory for kdump kernel can not be reserved as kdump kernel base is assumed to be 32MB always. When the kernel has CONFIG_RELOCATABLE option enabled, provide the feature to reserve the memory for kdump kernel anywhere in the RMO region. Hi Bernhard, Correct me if I'm wrong, but: CONFIG_RELOCATABLE is for the kernel that gets loaded as crashkernel, not for the kernel that loads the crashkernel. So it would be perfectly fine that a kernel that has not CONFIG_RELOCATABLE set would load another kernel that has CONFIG_RELOCATABLE set on an address != 32 M. No, with relocatable option, the same kernel is used as both production and kdump kernel. Can be, but it's not strictly necessary. It depends what userland does. Especially it's possible that a non-relocatable, self-compiled kernel loads a relocatable distribution kernel as capture kernel. Also, it would make sense to make the behaviour symmetric across platforms. Currently we have: - x86 and ia64: Without offset on command line, use any offset With offset on command line, use that offset and fail if no memory is available at that offset. - ppc64: Always use 32M and ignore the offset. If your patch gets applied, we have: - ppc64: With CONFIG_RELOCATABLE, use any offset With offset on command I don't see why the behaviour on ppc64 should be completely different. Having maintained kdump for SUSE for x86, ia64 and partly ppc64 in the past, I always felt that ppc64 is more different from x86 than ia64 is from x86. That's one more step into that direction without a technical reason. Having that all said: If your patch gets in mainline kernel, than we should change the behaviour also for x86 and ia64. Regards, Bernhard ___ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec
Re: [PATCH] Reserve memory for kdump kernel within RMO region
M. Mohan Kumar schrieb: Reserve memory for kdump kernel within RMO region When the kernel size exceeds 32MB(observed with some distros), memory for kdump kernel can not be reserved as kdump kernel base is assumed to be 32MB always. When the kernel has CONFIG_RELOCATABLE option enabled, provide the feature to reserve the memory for kdump kernel anywhere in the RMO region. Correct me if I'm wrong, but: CONFIG_RELOCATABLE is for the kernel that gets loaded as crashkernel, not for the kernel that loads the crashkernel. So it would be perfectly fine that a kernel that has not CONFIG_RELOCATABLE set would load another kernel that has CONFIG_RELOCATABLE set on an address != 32 M. So it would be part of the command line to determine whether a fixed or a variable address is used. The system configuration (or the admin) knows both: if the kernel that should be loaded is relocatable (can be detected with the x86 bzImage header or with the ELF type for vmlinux) and it can also influence the boot command line. To sum it up: I'm not against reserving it anywhere, I'm only against making it dependent on CONFIG_RELOCATABLE which has another function. Regards, Bernhard ___ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec
