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由 Andrey Ryabinin 提交于
KASAN fills kernel page tables with repeated values to map several TBs of the virtual memory to the single kasan_zero_page: kasan_zero_p4d -> kasan_zero_pud -> kasan_zero_pmd-> kasan_zero_pte-> kasan_zero_page Walking the whole KASAN shadow range takes a lot of time, especially with 5-level page tables. Since we already know that all kasan page tables eventually point to the kasan_zero_page we could call note_page() right and avoid walking lower levels of the page tables. This will not affect the output of the kernel_page_tables file, but let us avoid spending time in page table walkers: Before: $ time cat /sys/kernel/debug/kernel_page_tables > /dev/null real 0m55.855s user 0m0.000s sys 0m55.840s After: $ time cat /sys/kernel/debug/kernel_page_tables > /dev/null real 0m0.054s user 0m0.000s sys 0m0.054s Signed-off-by: NAndrey Ryabinin <aryabinin@virtuozzo.com> Acked-by: NKirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Alexander Potapenko <glider@google.com> Cc: Dmitry Vyukov <dvyukov@google.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/20170724152558.24689-1-aryabinin@virtuozzo.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
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