[ Adding David Woodhouse ] On Sat, Aug 15, 2015 at 1:59 AM, Christoph Hellwig <h...@lst.de> wrote: > On Fri, Aug 14, 2015 at 02:52:15PM -0700, Dan Williams wrote: >> The idea is that this memory is not meant to be available to the page >> allocator and should not count as new memory capacity. We're only >> hotplugging it to get struct page coverage. > > This might need a bigger audit of the max_pfn usages. I remember > architectures using it as a decisions for using IOMMUs or similar.
We chatted about this at LPC yesterday. The takeaway was that the max_pfn checks that the IOMMU code does is for checking whether a device needs an io-virtual mapping to reach addresses above its DMA limit (if it can't do 64-bit DMA). Given the capacities of persistent memory it's likely that a device with this limitation already can't address all of RAM let alone PMEM. So it seems to me that updating max_pfn for PMEM hotplug does not buy us anything except a few more opportunities to confuse PMEM as typical RAM. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
