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Subject: [PATCH v4 06/10] memory-hotplug.rst: add a note about ZONE_MOVABLE and page pinning
Date:   Thu, 17 Dec 2020 13:52:39 -0500
Message-Id: <20201217185243.3288048-7-pasha.tatashin@soleen.com>
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Document the special handling of page pinning when ZONE_MOVABLE present.

Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
Suggested-by: David Hildenbrand <david@redhat.com>
---
 Documentation/admin-guide/mm/memory-hotplug.rst | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst
index 5c4432c96c4b..c6618f99f765 100644
--- a/Documentation/admin-guide/mm/memory-hotplug.rst
+++ b/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
-- 
2.25.1