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    SubjectRE: [RFC PATCH] Add TRACE_IRQFLAGS_SUPPORT, LOCKDEP_SUPPORT then enable ftrace for ia64
    >> diff -BruN linux-2.6.31-rc6/arch/ia64/include/asm/page.h
    >> linux-2.6.31-rc6-lockdep/arch/ia64/include/asm/page.h
    >> --- linux-2.6.31-rc6/arch/ia64/include/asm/page.h 2009-08-13
    >> 15:43:34.000000000 -0700
    >> +++ linux-2.6.31-rc6-lockdep/arch/ia64/include/asm/page.h 2009-08-23
    >> 18:59:00.000000000 -0700
    >> @@ -41,7 +41,7 @@
    >> #define PAGE_SIZE (__IA64_UL_CONST(1) << PAGE_SHIFT)
    >> #define PAGE_MASK (~(PAGE_SIZE - 1))
    >>
    >> -#define PERCPU_PAGE_SHIFT 16 /* log2() of max. size of per-CPU area */
    >> +#define PERCPU_PAGE_SHIFT 20 /*16 log2() of max. size of per-CPU area */
    >> #define PERCPU_PAGE_SIZE (__IA64_UL_CONST(1) << PERCPU_PAGE_SHIFT)
    >
    > Why was this seemingly unrelated change done in a lockdep patch?

    IIRC it is because the lockdep code needs a lot more percpu memory than the
    64K that ia64 allocates.

    But I think that I'd prefer to only allocate the extra space when it
    is needed:

    #ifdef CONFIG_LOCKDEP
    #define PERCPU_PAGE_SHIFT 20 /* Need a Megabyte for lockdep */
    #else
    #define PERCPU_PAGE_SHIFT 16 /* 64K should be enough for normal use */
    #endif

    -Tony




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