On Tue, Jan 26, 2016 at 1:42 PM, Vlastimil Babka <vbabka(a)suse.cz> 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 :(
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
My initial implementation of ZONE_DEVICE ran into this conflict when
ZONES_SHIFT is > 2, and I fell back to cannibalizing ZONE_DMA.