[PATCH 3/3] docs: hugetlbpage.rst: add hugetlb migration description

[Baolin Wang <baolin.wang@linux.alibaba.com>]

Add some description of the hugetlb migration strategy.

Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
---
 Documentation/admin-guide/mm/hugetlbpage.rst | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Documentation/admin-guide/mm/hugetlbpage.rst b/Documentation/admin-guide/mm/hugetlbpage.rst
index e4d4b4a8dc97..f34a0d798d5b 100644
--- a/Documentation/admin-guide/mm/hugetlbpage.rst
+++ b/Documentation/admin-guide/mm/hugetlbpage.rst
@@ -376,6 +376,13 @@ Note that the number of overcommit and reserve pages remain global quantities,
 as we don't know until fault time, when the faulting task's mempolicy is
 applied, from which node the huge page allocation will be attempted.
 
+The hugetlb may be migrated between the per-node hugepages pool in the following
+scenarios: memory offline, memory failure, longterm pinning, syscalls(mbind,
+migrate_pages and move_pages), alloc_contig_range() and alloc_contig_pages().
+Now only memory offline, memory failure and syscalls allow fallbacking to allocate
+a new hugetlb on a different node if the current node is unable to allocate during
+hugetlb migration, that means these 3 cases can break the per-node hugepages pool.
+
 .. _using_huge_pages:
 
 Using Huge Pages
-- 
2.39.3