[ Adding David Woodhouse ] On Sat, Aug 15, 2015 at 1:59 AM, Christoph Hellwig <hch@xxxxxx> 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, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>