On Tue, Jan 26, 2016 at 1:42 PM, Vlastimil Babka <vbabka@xxxxxxx> wrote: > On 26.1.2016 1:06, Dan Williams wrote: >> It appears devices requiring ZONE_DMA are still prevalent (see link >> below). For this reason the proposal to require turning off ZONE_DMA to >> enable ZONE_DEVICE is untenable in the short term. We want a single >> kernel image to be able to support legacy devices as well as next >> generation persistent memory platforms. >> >> Towards this end, alias ZONE_DMA and ZONE_DEVICE to work around needing >> to maintain a unique zone number for ZONE_DEVICE. Record the geometry >> of ZONE_DMA at init (->init_spanned_pages) and use that information in >> is_zone_device_page() to differentiate pages allocated via >> devm_memremap_pages() vs true ZONE_DMA pages. Otherwise, use the >> simpler definition of is_zone_device_page() when ZONE_DMA is turned off. >> >> Note that this also teaches the memory hot remove path that the zone may >> not have sections for all pfn spans (->zone_dyn_start_pfn). >> >> A user visible implication of this change is potentially an unexpectedly >> high "spanned" value in /proc/zoneinfo for the DMA zone. > > [+CC Joonsoo, Laura] > > Sounds like quite a hack :( Indeed... > Would it be possible to extend the bits encoding > zone? Potentially, ZONE_CMA could be added one day... Not without impacting the ability to quickly lookup the numa node and parent section for a page. See ZONES_WIDTH, NODES_WIDTH, and SECTIONS_WIDTH. My initial implementation of ZONE_DEVICE ran into this conflict when ZONES_SHIFT is > 2, and I fell back to cannibalizing ZONE_DMA. -- 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>