Hi, I have a proposal to do crashdump without reserving memory during system boot. The method is as follow: 1. Do not reserve memory during system boot, that is crashkernel=<XX>@<YY> is not used in kernel command line. 2. A new kexec flag named KEXEC_CRASH_BY_NORMAL is defined for sys_kexec_load system call. When this flag is specified, the sys_kexec_load works as normal kexec (not crash kexec), except the destination image is kexec_crash_image instead of kexec_image. 3. In kexec-tools (/sbin/kexec), --mem-min=<addr1> and --mem-max=<addr2> is used to specify the memory area used by crashdump kernel. That is, the image, elf core header, available memory of crashdump kernel is within <addr1> ~ <addr2>. 4. In kexec-tools, in addition to kernel image, elf core header, etc are loaded, the available memory of crashdump kernel is loaded too. For example, the segments for sys_kexec_load for crashdump kernel can be: --mem-min=0x100000 --mem-max=0xffffff No. buf bufsz mem memsz 0 NULL 0 0x1000 0x9e000 1 0x881fe88 0x289b 0x100000 0x3000 2 NULL 0 0x103000 0xfd000 3 0xb7bfa808 0xb7c00 0x200000 0xb8000 4 NULL 0 0x2b8000 0xd39000 5 0x8818d38 0x7120 0xff1000 0x9000 6 NULL 0 0xffa000 0x1000 7 0x8818268 0x400 0xffb000 0x4000 8 NULL 0 0xfff000 0x1000 5. In relocate_kernel of Linux kernel, instead of copy the source page to destination page, the contents of source page and the destination page are swapped. (The destination page -> source page map is in kexec_crash_image->head) The memory area used by crashdump kernel is backupped to source page. In original crashdump implementation, the crashdump kernel run in reserved memory area. The reserved memory pages are reserved memory pages in primary (original) kernel. In this proposed implementation, the crashdump kernel run in specified memory area, the contents of destination memory area is backupped before crashdump kernel running. The backup pages are allocated memory pages in primary (original) kernel. The pros and cons of proposed implementation: Pros: - The memory used by crashdump kernel need not to be reserved during boot time. - The memory used by crashdump kernel can be specified during sys_kexec_load - The memory used by crashdump kernel can be freed after unloading. Cons: - The memory used by crashdump kernel can be the DMA destination, their contents may be ruined by devices during the boot of crashdump kernel. (Is it possible to turn off DMA for some memory area other than reserving it?) In fact, almost all mechanism for this proposal has been implemented by my previous patch: "kexec jump" in "kexec based hibernation". Any comment is welcome. Best Regards, Huang Ying
