Re: Kdump issue with percpu_alloc=lpage

[John Blackwood <john.blackwood@ccur.com>]

 > Subject: Re: Kdump issue with percpu_alloc=lpage
 > From: Vivek Goyal <vgoyal@redhat.com>
 > Date: Tue, 27 Oct 2009 15:24:14 -0400
 > To: "Blackwood, John" <john.blackwood@ccur.com>
 > CC: Tejun Heo <tj@kernel.org>, "kexec@lists.infradead.org" 
<kexec@lists.infradead.org>
 >
 > > > The lpage allocator is gone in the latest tree and only "embed" and
 > > > "page" allocators are there.  The only difference between the two is
 > > > that the embed one will put the first chunk inside the linearly 
mapped
 > > > area which in turn means that __pa() would work on static percpu
 > > > variables and some of dynamic ones but from the second chunk on and
 > > > for the page allocator, the percpu addresses will be remapped into
 > > > vmalloc area and behaves just like any other vmalloc address meaning
 > > > that the physical page can be determined using vmalloc_to_page(). 
  So,
 > > > something like the following should work,
 > > >
 > > >         v = per_cpu_ptr(crash_notes, cpunum);
 > > >         if (v < VMALLOC_START || v >= VMALLOC_END)
 > > >                 p = __pa(v);
 > > >         else
 > > >                 p = page_to_phys(vmalloc_to_page(v));
 > > >
 > > > For the now removed lpage, it would be a bit difficult and we'll
 > > > probably need to add a dedicated function to percpu to determine the
 > > > physical address.  Hmmm... probably the right thing to do is to add
 > > > such function so that the user can simply call percpu_to_phys()
 > > > regardless of address?
 > >
 > > Hi Tejun,
 > >
 > > Just my 2 cent's worth...
 > >
 > > I like the idea of having a percpu_to_phys() function that others can
 > > call so that such detail are localized... and this also would tend to
 > > be maintained better over time, since it would be more visible being
 > > located near where the percpu support is implmented.
 > >
 > > Thank you for the information.
 >
 > Thanks Tejun. percpu_to_phys() makes sense to me also. John, would you
 > like to post a patch for this.

Hi Vivek,

I'm probably not really NUMA/vm savy enough to attempt a patch
for approval at LKML.

But maybe someone else more qualified can take up the cause.

Thanks.

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