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

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Date:	Thu, 19 Feb 2009 22:44:14 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Tejun Heo <tj@...nel.org>, 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

On Thursday 19 February 2009 21:36:31 Ingo Molnar wrote:
> 
> * Rusty Russell <rusty@...tcorp.com.au> wrote:
> 
> > On Thursday 19 February 2009 00:13:31 Ingo Molnar wrote:
> > > 
> > > * Tejun Heo <tj@...nel.org> wrote:
> > > 
> > > >   0001-vmalloc-call-flush_cache_vunmap-from-unmap_kernel.patch
> > > >   0002-module-fix-out-of-range-memory-access.patch
> > > 
> > > Hm, these two seem to be .29 material too, agreed?
> > > 
> > > 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,
Rusty.
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