Re: [GIT RFC] percpu: use dynamic percpu allocator as the defaultpercpu allocator

[Tejun Heo]

Martin Schwidefsky wrote:
> On Wed, 25 Mar 2009 20:51:31 +0900
> Tejun Heo <tj@xxxxxxxxxx> wrote:
> 
>>> With your patches and a RELOC_HIDE version that uses the GOTENT
>>> indirection the kernel won't compile because the "X" constraint for
>>> the GOTENT access needs a symbol and there are quite a few users that
>>> pass a pointer. I do not see a simple solution for that problem yet.
>> Ah... okay.  Now I get it.  It wasn't expecting variables there.  How
>> about doing the following?
>>
>>  #define SHIFT_PERCPU_PTR(ptr, offset) (({				\
>> 	 if (__builtin_constant_p(ptr))					\
>> 		 do GOTENT trick;					\
>> 	 else								\
>> 		 RELOC_HIDE();						\
>>  }))
> 
> That doesn't work because __builtin_constant_p is false for variable
> symbols. I would need a __builtin_symbol_p but that doesn't exist.

Right, I somehow always get confused about the two.  Eh... Not easy.
I think alpha might have the same problem too.  I suppose we'll have
to make the legacy allocator available for alpha and s390 for the time
being.  I'll get to that.

Thanks.

-- 
tejun
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