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authorPeter Wemm <peter@FreeBSD.org>2006-04-21 04:24:50 +0000
committerPeter Wemm <peter@FreeBSD.org>2006-04-21 04:24:50 +0000
commitc0345a84aa23b03722ff306af87132e645f730c1 (patch)
tree97a80956c4bde01ad6fd8e57788220164a65b481 /sys/vm/vm_page.c
parent4f00efe0cb7026266afbed06abc58ee6f7ab8600 (diff)
downloadsrc-c0345a84aa23b03722ff306af87132e645f730c1.tar.gz
src-c0345a84aa23b03722ff306af87132e645f730c1.zip
Introduce minidumps. Full physical memory crash dumps are still available
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.
Notes
Notes: svn path=/head/; revision=157908
Diffstat (limited to 'sys/vm/vm_page.c')
-rw-r--r--sys/vm/vm_page.c21
1 files changed, 21 insertions, 0 deletions
diff --git a/sys/vm/vm_page.c b/sys/vm/vm_page.c
index f84efa59e7a1..05123473f764 100644
--- a/sys/vm/vm_page.c
+++ b/sys/vm/vm_page.c
@@ -121,6 +121,8 @@ __FBSDID("$FreeBSD$");
#include <vm/uma.h>
#include <vm/uma_int.h>
+#include <machine/md_var.h>
+
/*
* Associated with page of user-allocatable memory is a
* page structure.
@@ -232,6 +234,25 @@ vm_page_startup(vm_offset_t vaddr)
bzero((void *)mapped, end - new_end);
uma_startup((void *)mapped, boot_pages);
+#if defined(__amd64__) || defined(__i386__)
+ /*
+ * Allocate a bitmap to indicate that a random physical page
+ * needs to be included in a minidump.
+ *
+ * The amd64 port needs this to indicate which direct map pages
+ * need to be dumped, via calls to dump_add_page()/dump_drop_page().
+ *
+ * However, i386 still needs this workspace internally within the
+ * minidump code. In theory, they are not needed on i386, but are
+ * included should the sf_buf code decide to use them.
+ */
+ page_range = phys_avail[(nblocks - 1) * 2 + 1] / PAGE_SIZE;
+ vm_page_dump_size = round_page(roundup2(page_range, NBBY) / NBBY);
+ new_end -= vm_page_dump_size;
+ vm_page_dump = (void *)(uintptr_t)pmap_map(&vaddr, new_end,
+ new_end + vm_page_dump_size, VM_PROT_READ | VM_PROT_WRITE);
+ bzero((void *)vm_page_dump, vm_page_dump_size);
+#endif
/*
* Compute the number of pages of memory that will be available for
* use (taking into account the overhead of a page structure per