Changelog v1 - v2 - No changes to patches, addressed suggestion from James Morse to add "arm64" tag to cover letter. - Improved cover letter information based on discussion. Currently, it is only allowed to reserve memory for crash kernel, because it is a requirement in order to be able to boot into crash kernel without touching memory of crashed kernel is to have memory reserved. The second benefit for having memory reserved for kexec kernel is that it does not require a relocation after segments are loaded into memory. If kexec functionality is used for a fast system update, with a minimal downtime, the relocation of kernel + initramfs might take a significant portion of reboot. In fact, on the machine that we are using, that has ARM64 processor it takes 0.35s to relocate during kexec, thus taking 52% of kernel reboot time: kernel shutdown 0.03s relocation 0.35s kernel startup 0.29s Image: 13M and initramfs is 24M. If initramfs increases, the relocation time increases proportionally. While, it is possible to add 'kexeckernel=' parameters support to other architectures by modifying reserve_crashkernel(), in this series this is done for arm64 only. The reason it is so slow on arm64 to relocate kernel is because the code that does relocation does this with MMU disabled, and thus D-Cache and I-Cache must also be disabled. Alternative solution is more complicated: Setup a temporary page table for relocation_routine and also for code from cpu_soft_restart. Perform relocation with MMU enabled, do cpu_soft_restart where MMU and caching are disabled, jump to purgatory. A similar approach was suggested for purgatory and was rejected due to making purgatory too complicated. On, the other hand hibernate does something similar already, but there MMU never needs to be disabled, and also by the time machine_kexec() is called, allocator is not available, as we can't fail to do reboot, so page table must be pre-allocated during kernel load time. Note: the above time is relocation time only. Purgatory usually also computes checksum, but that is skipped, because --no-check is used when kernel image is loaded via kexec. Pavel Tatashin (5): kexec: quiet down kexec reboot kexec: add resource for normal kexec region kexec: export common crashkernel/kexeckernel parser kexec: use reserved memory for normal kexec reboot arm64, kexec: reserve kexeckernel region .../admin-guide/kernel-parameters.txt | 7 ++ arch/arm64/kernel/setup.c | 5 ++ arch/arm64/mm/init.c | 83 ++++++++++++------- include/linux/crash_core.h | 6 ++ include/linux/ioport.h | 1 + include/linux/kexec.h | 6 +- kernel/crash_core.c | 27 +++--- kernel/kexec_core.c | 50 +++++++---- 8 files changed, 127 insertions(+), 58 deletions(-) -- 2.22.0 _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
