Re: [Fastboot] [PATCH] Reserving backup region for kexec basedcrashdumps.
From: Vivek Goyal
Date: Tue Feb 01 2005 - 09:28:29 EST
Well, trying to put the already discussed ideas together. I was
planning to work on following design. Please comment.
Crashed Kernel <-->Capture Kernel(or User Space) Interface:
The whole idea is that Crash image is represented in ELF Core format.
These ELF Headers are prepared by kexec-tools user space and put in one
segment. Address of start of image is passed to the capture kernel(or
user space) using one command line (eg. crashimage=). Now either kernel
space or user space can parse the elf headers and extract required
information and export final kernel elf core image.
> ebiederm@xxxxxxxxxxxx wrote:
> If we were using an ELF header I would include one PT_NOTE program
> header per cpu (Giving each cpu it's own area to mess around in).
> And I would use one PT_LOAD segment per possible memory zone.
> So in the worst case (current sgi altix) (MAX_NUMNODES=256,
> MAX_NR_ZONES=3, MAX_NR_CPUS=1024) 256*3+1024 = 1792 program
> headers. At 56 bytes per 64bit program header that is 100352 bytes
> or 98KiB. A little bit expensive. A tuned data structure with
> 64bit base and size would only consume 1792*16 = 28672 or 28KiB.
If I prepare One elf header for each physical contiguous memory area (as
obtained from /proc/iomem) instead of per zone, then number of elf
headers will come down significantly. I don't have any idea on number of
actual physically contiguous regions present per machine, but roughly
assuming it to be 1 per node, it will lead to 256 + 1024 = 1280 program
headers.At 56 bytes per 64 bit program header this will amount to 70KB.
This is worst case estimate and on lower end machines this will require
much less a space. On machines as big as 1024 cpus, this should not be a
concern, as big machines come with big RAMs.
Eric, do you still think that ELF headers are inappropriate to be passed
across interface boundary.
ELF headers can be prepared by kexec-tools in advance and put into one
of the data segments. This requires following information to be
available to user space.
- Starting address of space reserved by kernel for notes section
(crash_notes). Probably can be obtained from /proc/kallsysms?
- NR_CPUS. May be sysconf(_SC_NPROCESSORS_CONF) should be sufficient.
- Size of memory reserved per cpu. No clue how to get that? Any
May be hard-coding like 1K area per cpu should be to address the
future needs ?
Regarding Backup Region
- Kexec user space does the reservation for backup region segment.
- Purgatory copies the backup data to backup region. (Already
- A separate elf header is prepared to represent backed up memory
region. And "offset" field of this program header can contain the actual
physical address where backup contents are stored.
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