Messages in this thread | | | Date | Fri, 12 Mar 2010 19:09:41 -0800 | From | Andi Kleen <> | Subject | Re: swiotlb detection should be memory hotplug aware ? |
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, Alok Kataria wrote:
Hi Alok,
> Hi, > > Looking at the current code swiotlb is initialized for 64bit kernels > only when the max_pfn value is greater than 4G (MAX_DMA32_PFN value). > So in cases when the initial memory is less than 4GB the kernel boots > without enabling swiotlb, when we hotadd memory to such a kernel and go > beyond the 4G limit, swiotlb is still disabled. As a result when any > 32bit devices start using this newly added memory beyond 4G, the kernel > starts spitting error messages like below or in some cases it causes > kernel panics.
Yes seems like a real problem.
> > 1. Enable swiotlb for all 64bit kernels which have memory hot-add > support.
I don't think that's a good idea. It would enable it everywhere on distributions which compile with hotadd. Need (2)
> 2. Instead of checking the max_pfn value in pci_swiotlb_detect, check > for max_hotpluggable_pfn (or some such) value. Though I don't see such a > value readily available. I could parse the SRAT and get hotplug memory > information but that will make swiotlb detection logic a little too > complex. A quick look around srat_xx.c files and the acpi_memhotplug > module didn't find any useful API that could be used directly either. > So was wondering if any of you are aware of an easy way to get such > information ?
I have a patchkit to revamp the SRAT parsing to store the hotadd information more efficiently (the current way is pretty dumb) I need to repost that.
With that it would be relatively easy to do I think.
-Andi
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