Re: [PATCHSET x86/core/percpu] implement dynamic percpu allocator

[Tejun Heo <tj@kernel.org>]

Rusty Russell wrote:
>>>> Rusty, if the fixes are fine with you i can put those two 
>>>> commits into tip/core/urgent straight away, the full string of 
>>>> 10 commits into tip/core/percpu and thus we'd avoid duplicate 
>>>> (or even conflicting) commits.
>>> No, the second one is not .29 material; it's a nice, but 
>>> theoretical, fix.
>> Can it never trigger?
> 
> Actually, checked again.  It's not even necessary AFAICT (tho a comment
> would be nice):
> 
> 	for (i = 0; i < pcpu_num_used; ptr += block_size(pcpu_size[i]), i++) {
> 		/* Extra for alignment requirement. */
> 		extra = ALIGN((unsigned long)ptr, align) - (unsigned long)ptr;
> 		BUG_ON(i == 0 && extra != 0);
> 
> 		if (pcpu_size[i] < 0 || pcpu_size[i] < extra + size)
> 			continue;
> 
> 		/* Transfer extra to previous block. */
> 		if (pcpu_size[i-1] < 0)
> 			pcpu_size[i-1] -= extra;
> 		else
> 			pcpu_size[i-1] += extra;
> 
> pcpu_size[0] is *always* negative: it's marked allocated at initialization
> (it's the static per-cpu allocations).
> 
> Sorry I didn't examine more closely,

Ah... okay.  Right.  I took the code and used it in the chunk area
allocator where 0 isn't guaranteed to be occupied and saw the problem
triggering and then assumed the modalloc allocator shared the same
problem.  So, unnecessary fix but I think it really needs some
explanation.

What to do about #tj-percpu?  Ingo, do you want me to rebase tree sans
the second one?

Thanks.

-- 
tejun