Re: [PATCH V4 1/1] rcu: introduce kfree_rcu()

[Arnd Bergmann]

On Tuesday 15 March 2011 10:46:20 Lai Jiangshan wrote:
> +static __always_inline bool __is_kfree_rcu_offset(unsigned long offset)
> +{
> +       return offset < 4096;
> +}

So this relies on the assumptions that 

a) the rcu_head is within the first 4 KB of the data structure to be freed
b) no callback ever gets called in the first 4 KB of virtual address space

It's probably a reasonable assumption, but I think it should be documented
more explicitly, especially the first one. It's entirely possible that
an RCU managed data structure is larger than 4 KB.
Another alternative might be to encode the difference between a
function pointer and an offset in one of the lower bits of the address.

	Arnd
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