[v2,0/5] mm: Fix pfn_to_online_page() with respect to ZONE_DEVICE

Message

Dan Williams Jan. 12, 2021, 9:34 a.m. UTC

Changes since v1 [1]:
- Clarify the failing condition in patch 3 (Michal)
- Clarify how subsection collisions manifest in shipping systems
  (Michal)
- Use zone_idx() (Michal)
- Move section_taint_zone_device() conditions to
  move_pfn_range_to_zone() (Michal)
- Fix pfn_to_online_page() to account for pfn_valid() vs
  pfn_section_valid() confusion (David)

[1]: http://lore.kernel.org/r/[e-mail]

---

Michal reminds that the discussion about how to ensure pfn-walkers do
not get confused by ZONE_DEVICE pages never resolved. A pfn-walker that
uses pfn_to_online_page() may inadvertently translate a pfn as online
and in the page allocator, when it is offline managed by a ZONE_DEVICE
mapping (details in Patch 3: ("mm: Teach pfn_to_online_page() about
ZONE_DEVICE section collisions")).

The 2 proposals under consideration are teach pfn_to_online_page() to be
precise in the presence of mixed-zone sections, or teach the memory-add
code to drop the System RAM associated with ZONE_DEVICE collisions. In
order to not regress memory capacity by a few 10s to 100s of MiB the
approach taken in this set is to add precision to pfn_to_online_page().

In the course of validating pfn_to_online_page() a couple other fixes
fell out:

1/ soft_offline_page() fails to drop the reference taken in the
   madvise(..., MADV_SOFT_OFFLINE) case.

2/ The libnvdimm sysfs attribute visibility code was failing to publish
   the resource base for memmap=ss!nn defined namespaces. This is needed
   for the regression test for soft_offline_page().

---

Dan Williams (5):
      mm: Move pfn_to_online_page() out of line
      mm: Teach pfn_to_online_page() to consider subsection validity
      mm: Teach pfn_to_online_page() about ZONE_DEVICE section collisions
      mm: Fix page reference leak in soft_offline_page()
      libnvdimm/namespace: Fix visibility of namespace resource attribute


 drivers/nvdimm/namespace_devs.c |   10 +++---
 include/linux/memory_hotplug.h  |   17 +----------
 include/linux/mmzone.h          |   22 +++++++++-----
 mm/memory-failure.c             |   20 ++++++++++---
 mm/memory_hotplug.c             |   62 +++++++++++++++++++++++++++++++++++++++
 5 files changed, 99 insertions(+), 32 deletions(-)