diff options
| author | Olaf Hering <olaf@aepfle.de> | 2011-05-26 16:25:54 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2011-05-26 17:12:37 -0700 |
| commit | 997c136f518c5debd63847e78e2a8694f56dcf90 (patch) | |
| tree | ac2ff48901be3e6834757675dcc177732e034a9f /include/linux | |
| parent | 98bc93e505c03403479c6669c4ff97301cee6199 (diff) | |
fs/proc/vmcore.c: add hook to read_from_oldmem() to check for non-ram pages
The balloon driver in a Xen guest frees guest pages and marks them as
mmio. When the kernel crashes and the crash kernel attempts to read the
oldmem via /proc/vmcore a read from ballooned pages will generate 100%
load in dom0 because Xen asks qemu-dm for the page content. Since the
reads come in as 8byte requests each ballooned page is tried 512 times.
With this change a hook can be registered which checks wether the given
pfn is really ram. The hook has to return a value > 0 for ram pages, a
value < 0 on error (because the hypercall is not known) and 0 for non-ram
pages.
This will reduce the time to read /proc/vmcore. Without this change a
512M guest with 128M crashkernel region needs 200 seconds to read it, with
this change it takes just 2 seconds.
Signed-off-by: Olaf Hering <olaf@aepfle.de>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/linux')
| -rw-r--r-- | include/linux/crash_dump.h | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/include/linux/crash_dump.h b/include/linux/crash_dump.h index 088cd4ace4e..74054074e87 100644 --- a/include/linux/crash_dump.h +++ b/include/linux/crash_dump.h @@ -66,6 +66,11 @@ static inline void vmcore_unusable(void) if (is_kdump_kernel()) elfcorehdr_addr = ELFCORE_ADDR_ERR; } + +#define HAVE_OLDMEM_PFN_IS_RAM 1 +extern int register_oldmem_pfn_is_ram(int (*fn)(unsigned long pfn)); +extern void unregister_oldmem_pfn_is_ram(void); + #else /* !CONFIG_CRASH_DUMP */ static inline int is_kdump_kernel(void) { return 0; } #endif /* CONFIG_CRASH_DUMP */ |