On Tue, Aug 18, 2015 at 9:55 AM, Jerome Glisse <j.glisse@xxxxxxxxx> wrote: > On Mon, Aug 17, 2015 at 05:46:43PM -0700, Dan Williams wrote: >> On Mon, Aug 17, 2015 at 2:45 PM, Jerome Glisse <j.glisse@xxxxxxxxx> wrote: >> > On Fri, Aug 14, 2015 at 07:11:27PM -0700, Dan Williams wrote: >> >> 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. >> > >> > So i attach is a patch that should keep ZONE_DEVICE out of consideration >> > for the buddy allocator. You might also want to keep page reserved and not >> > free inside the zone, you could replace the generic_online_page() using >> > set_online_page_callback() while hotpluging device memory. >> > >> >> Hmm, are we already protected by the fact that ZONE_DEVICE is not >> represented in the GFP_ZONEMASK? > > Yeah seems you right, high_zoneidx (which is derive using gfp_zone()) will > always limit which zones are considered. I thought that under memory presure > it would go over all of the zonelist entry and eventualy consider the device > zone. But it doesn't seems to be that way. > > Keeping the device zone out of the zonelist might still be a good idea, if > only to avoid pointless iteration for the page allocator. Unless someone can > think of a reason why this would be bad. > The other question I have is whether disabling ZONE_DMA is a realistic tradeoff for enabling ZONE_DEVICE? I.e. can ZONE_DMA default to off going forward, lose some ISA device support, or do we need to figure out how to enable > 4 zones. -- 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>