From 997c136f518c5debd63847e78e2a8694f56dcf90 Mon Sep 17 00:00:00 2001 From: Olaf Hering Date: Thu, 26 May 2011 16:25:54 -0700 Subject: 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 Cc: Alexey Dobriyan Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/crash_dump.h | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'include/linux') diff --git a/include/linux/crash_dump.h b/include/linux/crash_dump.h index 088cd4ace4ef..74054074e876 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 */ -- cgit v1.2.2