** Also affects: linux (Ubuntu Artful)
Importance: Undecided
Status: New
** Changed in: linux (Ubuntu Artful)
Importance: Undecided => High
** Changed in: linux (Ubuntu Artful)
Status: New => In Progress
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https://bugs.launchpad.net/bugs/1761104
Title:
fix regression in mm/hotplug, allows NVIDIA driver to work
Status in linux package in Ubuntu:
In Progress
Status in linux source package in Artful:
In Progress
Bug description:
== SRU Justification, ARTFUL ==
Bug fix #1747069 causes an issue for NVIDIA drivers on ppc64el
platforms. According to Will Davis at NVIDIA:
"- The original patch 3d79a728f9b2e6ddcce4e02c91c4de1076548a4c changed
the call to arch_add_memory in mm/memory_hotplug.c to call with the
boolean argument set to true instead of false, and inverted the
semantics of that argument in the arch layers.
- The revert patch 4fe85d5a7c50f003fe4863a1a87f5d8cc121c75c reverted
the semantic change in the arch layers, but didn't revert the change
to the arch_add_memory call in mm/memory_hotplug.c"
And also:
"It looks like the problem here is that the online_type is _MOVABLE but
can_online_high_movable(nid=255) is returning false:
if ((zone_idx(zone) > ZONE_NORMAL ||
online_type == MMOP_ONLINE_MOVABLE) &&
!can_online_high_movable(pfn_to_nid(pfn)))
This check was removed by upstream commit
57c0a17238e22395428248c53f8e390c051c88b8, and I've verified that if I apply
that commit (partially) to the 4.13.0-37.42 tree along with the previous
arch_add_memory patch to make the probe work, I can fully online the GPU
device
memory as expected.
Commit 57c0a172.. implies that the can_online_high_movable() checks weren't
useful anyway, so in addition to the arch_add_memory fix, does it make sense
to
revert the pieces of 4fe85d5a7c50f003fe4863a1a87f5d8cc121c75c that added back
the can_online_high_movable() check?"
== Fix ==
Fix partial backport from bug #1747069, remove can_online_high_movable
and fix the incorrectly set boolean argument to arch_add_memory().
== Regression Potential ==
This fixes a regression in the original fix and hence the regression
potential is the same as the previously SRU'd bug fix for #1747069,
namely:
"Reverting this commit does remove some functionality, however this
does not regress the kernel compared to previous releases and having a
working reliable memory hotplug is the preferred option. This fix does
touch some memory hotplug, so there is a risk that this may break this
functionality that is not covered by the kernel regression testing."
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