The patch titled
Subject: memory-hotplug.rst: add a note about ZONE_MOVABLE and page pinning
has been added to the -mm tree. Its filename is
memory-hotplugrst-add-a-note-about-zone_movable-and-page-pinning.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/memory-hotplugrst-add-a-note-about-zone_movable-and-page-pinning.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/memory-hotplugrst-add-a-note-about-zone_movable-and-page-pinning.patch
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------------------------------------------------------
From: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
Subject: memory-hotplug.rst: add a note about ZONE_MOVABLE and page pinning
Document the special handling of page pinning when ZONE_MOVABLE present.
Link: https://lkml.kernel.org/r/20210201153827.444374-11-pasha.tatashin@xxxxxxxxxx
Signed-off-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
Cc: James Morris <jmorris@xxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Sasha Levin <sashal@xxxxxxxxxx>
Cc: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Cc: Tyler Hicks <tyhicks@xxxxxxxxxxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/admin-guide/mm/memory-hotplug.rst | 9 +++++++++
1 file changed, 9 insertions(+)
--- a/Documentation/admin-guide/mm/memory-hotplug.rst~memory-hotplugrst-add-a-note-about-zone_movable-and-page-pinning
+++ a/Documentation/admin-guide/mm/memory-hotplug.rst
@@ -357,6 +357,15 @@ creates ZONE_MOVABLE as following.
Unfortunately, there is no information to show which memory block belongs
to ZONE_MOVABLE. This is TBD.
+.. note::
+ Techniques that rely on long-term pinnings of memory (especially, RDMA and
+ vfio) are fundamentally problematic with ZONE_MOVABLE and, therefore, memory
+ hot remove. Pinned pages cannot reside on ZONE_MOVABLE, to guarantee that
+ memory can still get hot removed - be aware that pinning can fail even if
+ there is plenty of free memory in ZONE_MOVABLE. In addition, using
+ ZONE_MOVABLE might make page pinning more expensive, because pages have to be
+ migrated off that zone first.
+
.. _memory_hotplug_how_to_offline_memory:
How to offline memory
_
Patches currently in -mm which might be from pasha.tatashin@xxxxxxxxxx are
mm-gup-dont-pin-migrated-cma-pages-in-movable-zone.patch
mm-gup-check-every-subpage-of-a-compound-page-during-isolation.patch
mm-gup-return-an-error-on-migration-failure.patch
mm-gup-check-for-isolation-errors.patch
mm-cma-rename-pf_memalloc_nocma-to-pf_memalloc_pin.patch
mm-apply-per-task-gfp-constraints-in-fast-path.patch
mm-honor-pf_memalloc_pin-for-all-movable-pages.patch
mm-gup-do-not-migrate-zero-page.patch
mm-gup-migrate-pinned-pages-out-of-movable-zone.patch
memory-hotplugrst-add-a-note-about-zone_movable-and-page-pinning.patch
mm-gup-change-index-type-to-long-as-it-counts-pages.patch
mm-gup-longterm-pin-migration-cleanup.patch
selftests-vm-gup_test-fix-test-flag.patch
selftests-vm-gup_test-test-faulting-in-kernel-and-verify-pinnable-pages.patch
