On Fri, Aug 14, 2015 at 3:33 PM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote: > On Fri, Aug 14, 2015 at 3:06 PM, Jerome Glisse <j.glisse@xxxxxxxxx> wrote: >> On Fri, Aug 14, 2015 at 02:52:15PM -0700, Dan Williams wrote: >>> On Fri, Aug 14, 2015 at 2:37 PM, Jerome Glisse <j.glisse@xxxxxxxxx> wrote: >>> > On Wed, Aug 12, 2015 at 11:50:05PM -0400, Dan Williams wrote: > [..] >>> > What is the rational for not updating max_pfn, max_low_pfn, ... ? >>> > >>> >>> 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. >> >> But this sounds bogus to me to rely on max_pfn to stay smaller than >> first_dev_pfn. For instance you might plug a device that register >> dev memory and then some regular memory might be hotplug, effectively >> updating max_pfn to a value bigger than first_dev_pfn. >> > > True. > >> Also i do not think that the buddy allocator use max_pfn or max_low_pfn >> to consider page/zone for allocation or not. > > Yes, I took it out with no effects. I'll investigate further whether > we should be touching those variables or not for this new usage. Although it does not offer perfect protection if device memory is at a physically lower address than RAM, skipping the update of these variables does seem to be what we want. For example /dev/mem would fail to allow write access to persistent memory if it fails a valid_phys_addr_range() check. Since /dev/mem does not know how to write to PMEM in a reliably persistent way, it should not treat a PMEM-pfn like 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>