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

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Message-ID: <499E4142.8020907@kernel.org>
Date:	Fri, 20 Feb 2009 14:36:02 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Rusty Russell <rusty@...tcorp.com.au>
CC:	Ingo Molnar <mingo@...e.hu>, tglx@...utronix.de, x86@...nel.org,
	linux-kernel@...r.kernel.org, hpa@...or.com, jeremy@...p.org,
	cpw@....com
Subject: Re: [PATCHSET x86/core/percpu] implement dynamic percpu allocator

Tejun Heo wrote:
> 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?

Ingo, as you haven't pulled already.  I'm incorporating changes from
the comments posted till now and rebasing the tree.  Please stand by a
bit.

Thanks.

-- 
tejun
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