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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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