dbae6322e8
via the debug.minidump sysctl and tunable. Traditional dumps store all physical memory. This was once a good thing when machines had a maximum of 64M of ram and 1GB of kvm. These days, machines often have many gigabytes of ram and a smaller amount of kvm. libkvm+kgdb don't have a way to access physical ram that is not mapped into kvm at the time of the crash dump, so the extra ram being dumped is mostly wasted. Minidumps invert the process. Instead of dumping physical memory in in order to guarantee that all of kvm's backing is dumped, minidumps instead dump only memory that is actively mapped into kvm. amd64 has a direct map region that things like UMA use. Obviously we cannot dump all of the direct map region because that is effectively an old style all-physical-memory dump. Instead, introduce a bitmap and two helper routines (dump_add_page(pa) and dump_drop_page(pa)) that allow certain critical direct map pages to be included in the dump. uma_machdep.c's allocator is the intended consumer. Dumps are a custom format. At the very beginning of the file is a header, then a copy of the message buffer, then the bitmap of pages present in the dump, then the final level of the kvm page table trees (2MB mappings are expanded into a 4K page mappings), then the sparse physical pages according to the bitmap. libkvm can now conveniently access the kvm page table entries. Booting my test 8GB machine, forcing it into ddb and forcing a dump leads to a 48MB minidump. While this is a best case, I expect minidumps to be in the 100MB-500MB range. Obviously, never larger than physical memory of course. minidumps are on by default. It would want be necessary to turn them off if it was necessary to debug corrupt kernel page table management as that would mess up minidumps as well. Both minidumps and regular dumps are supported on the same machine. |
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| .. | ||
| defines | ||
| files | ||
| files.alpha | ||
| files.amd64 | ||
| files.arm | ||
| files.i386 | ||
| files.ia64 | ||
| files.pc98 | ||
| files.powerpc | ||
| files.sparc64 | ||
| kern.mk | ||
| kern.post.mk | ||
| kern.pre.mk | ||
| kmod_syms.awk | ||
| kmod.mk | ||
| ldscript.alpha | ||
| ldscript.amd64 | ||
| ldscript.arm | ||
| ldscript.i386 | ||
| ldscript.ia64 | ||
| ldscript.powerpc | ||
| ldscript.sparc64 | ||
| Makefile.alpha | ||
| Makefile.amd64 | ||
| Makefile.arm | ||
| Makefile.i386 | ||
| Makefile.ia64 | ||
| Makefile.pc98 | ||
| Makefile.powerpc | ||
| Makefile.sparc64 | ||
| makeLINT.mk | ||
| makeLINT.sed | ||
| newvers.sh | ||
| NOTES | ||
| options | ||
| options.alpha | ||
| options.amd64 | ||
| options.arm | ||
| options.i386 | ||
| options.ia64 | ||
| options.pc98 | ||
| options.powerpc | ||
| options.sparc64 | ||
| systags.sh | ||