> Subject: Re: Kdump issue with percpu_alloc=lpage > From: Vivek Goyal <vgoyal at redhat.com> > Date: Tue, 27 Oct 2009 15:24:14 -0400 > To: "Blackwood, John" <john.blackwood at ccur.com> > CC: Tejun Heo <tj at kernel.org>, "kexec at lists.infradead.org" <kexec at 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.
