On Mon, 25 Jan 2016 16:06:40 -0800 Dan Williams <dan.j.williams@xxxxxxxxx> 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. More than "short term". When can we ever nuke ZONE_DMA? This was a pretty big goof - the removal of ZONE_DMA whizzed straight past my attention, alas. In fact I never noticed the patch at all until I got some conflicts in -next a few weeks later (wasn't cc'ed). And then I didn't read the changelog closely enough. > We want a single > kernel image to be able to support legacy devices as well as next > generation persistent memory platforms. yup. > 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. Well, all these icky tricks are to avoid increasing ZONES_SHIFT, yes? Is it possible to just use ZONES_SHIFT=3? Also, this "dynamically added pfn of the zone" thing is a new concept and I think it should be more completely documented somewhere in the code. -- 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>