From fa965fd54827a6b6967602051736da9c163b79b7 Mon Sep 17 00:00:00 2001 From: Pavel Tatashin Date: Tue, 4 May 2021 18:39:12 -0700 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/20210215161349.246722-11-pasha.tatashin@soleen.com Signed-off-by: Pavel Tatashin Suggested-by: David Hildenbrand Acked-by: Michal Hocko Cc: Dan Williams Cc: David Rientjes Cc: Ingo Molnar Cc: Ira Weiny Cc: James Morris Cc: Jason Gunthorpe Cc: Jason Gunthorpe Cc: John Hubbard Cc: Joonsoo Kim Cc: Matthew Wilcox Cc: Mel Gorman Cc: Michal Hocko Cc: Mike Kravetz Cc: Oscar Salvador Cc: Peter Zijlstra Cc: Sasha Levin Cc: Steven Rostedt (VMware) Cc: Tyler Hicks Cc: Vlastimil Babka Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/admin-guide/mm/memory-hotplug.rst | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'Documentation/admin-guide/mm') diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst index 5307f90738aa..05d51d2d8beb 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 -- cgit v1.2.3