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    SubjectRE: [RFC PATCH] Add TRACE_IRQFLAGS_SUPPORT, LOCKDEP_SUPPORT then enable ftrace for ia64
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    On Wed, 2009-09-02 at 16:27 -0700, Luck, Tony wrote:
    > >> 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

    Hmm, isn't all that percpu stuff in a special section, who's size you
    can query at boot time and set-up accordingly?





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