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997c136f51
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>
80 lines
2.3 KiB
C
80 lines
2.3 KiB
C
#ifndef LINUX_CRASH_DUMP_H
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#define LINUX_CRASH_DUMP_H
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#ifdef CONFIG_CRASH_DUMP
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#include <linux/kexec.h>
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#include <linux/device.h>
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#include <linux/proc_fs.h>
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#define ELFCORE_ADDR_MAX (-1ULL)
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#define ELFCORE_ADDR_ERR (-2ULL)
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extern unsigned long long elfcorehdr_addr;
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extern ssize_t copy_oldmem_page(unsigned long, char *, size_t,
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unsigned long, int);
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/* Architecture code defines this if there are other possible ELF
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* machine types, e.g. on bi-arch capable hardware. */
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#ifndef vmcore_elf_check_arch_cross
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#define vmcore_elf_check_arch_cross(x) 0
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#endif
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/*
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* Architecture code can redefine this if there are any special checks
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* needed for 64-bit ELF vmcores. In case of 32-bit only architecture,
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* this can be set to zero.
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*/
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#ifndef vmcore_elf64_check_arch
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#define vmcore_elf64_check_arch(x) (elf_check_arch(x) || vmcore_elf_check_arch_cross(x))
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#endif
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/*
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* is_kdump_kernel() checks whether this kernel is booting after a panic of
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* previous kernel or not. This is determined by checking if previous kernel
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* has passed the elf core header address on command line.
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*
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* This is not just a test if CONFIG_CRASH_DUMP is enabled or not. It will
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* return 1 if CONFIG_CRASH_DUMP=y and if kernel is booting after a panic of
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* previous kernel.
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*/
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static inline int is_kdump_kernel(void)
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{
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return (elfcorehdr_addr != ELFCORE_ADDR_MAX) ? 1 : 0;
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}
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/* is_vmcore_usable() checks if the kernel is booting after a panic and
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* the vmcore region is usable.
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*
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* This makes use of the fact that due to alignment -2ULL is not
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* a valid pointer, much in the vain of IS_ERR(), except
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* dealing directly with an unsigned long long rather than a pointer.
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*/
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static inline int is_vmcore_usable(void)
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{
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return is_kdump_kernel() && elfcorehdr_addr != ELFCORE_ADDR_ERR ? 1 : 0;
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}
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/* vmcore_unusable() marks the vmcore as unusable,
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* without disturbing the logic of is_kdump_kernel()
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*/
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static inline void vmcore_unusable(void)
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{
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if (is_kdump_kernel())
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elfcorehdr_addr = ELFCORE_ADDR_ERR;
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}
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#define HAVE_OLDMEM_PFN_IS_RAM 1
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extern int register_oldmem_pfn_is_ram(int (*fn)(unsigned long pfn));
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extern void unregister_oldmem_pfn_is_ram(void);
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#else /* !CONFIG_CRASH_DUMP */
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static inline int is_kdump_kernel(void) { return 0; }
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#endif /* CONFIG_CRASH_DUMP */
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extern unsigned long saved_max_pfn;
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#endif /* LINUX_CRASHDUMP_H */
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