[v3,0/6] mm: Fix pfn_to_online_page() with respect to ZONE_DEVICE

Message

Dan Williams Jan. 13, 2021, 7:35 a.m. UTC

Changes since v2 [1]:
- Collect some reviewed-by's from David and Oscar

- Rework subsection validity to include pfn_valid() gated by
  CONFIG_HAVE_ARCH_PFN_VALID (David, Oscar)

- Introduce pgmap_pfn_valid() to validate metadata vs data in a pgmap (David)

! Kill put_ref_page(): the extra "if (ref_page) put_page(ref_page)" still
  feels more cluttered than adding a tiny helper. (Oscar)

[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().

3/ memory_failure() uses get_dev_pagemap() to lookup ZONE_DEVICE pages,
   however that mapping may contain data pages and metadata raw pfns.
   Introduce pgmap_pfn_valid() to delineate the 2 types and fail the
   handling of raw metadata pfns.

---

Dan Williams (6):
      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()
      mm: Fix memory_failure() handling of dax-namespace metadata
      libnvdimm/namespace: Fix visibility of namespace resource attribute


 drivers/nvdimm/namespace_devs.c |   10 +++---
 include/linux/memory_hotplug.h  |   17 +--------
 include/linux/memremap.h        |    6 +++
 include/linux/mmzone.h          |   22 ++++++++----
 mm/memory-failure.c             |   26 ++++++++++++--
 mm/memory_hotplug.c             |   70 +++++++++++++++++++++++++++++++++++++++
 mm/memremap.c                   |   15 ++++++++
 7 files changed, 134 insertions(+), 32 deletions(-)