On Mon, 25 Jan 2016 16:06:40 -0800 Dan Williams <dan.j.williams(a)intel.com> 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.
Towards this end, alias ZONE_DMA and ZONE_DEVICE to work around
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