[patch] mmap.2: document the munmap exception for underlying page size

[David Rientjes <rientjes@google.com>]

munmap(2) will fail with an errno of EINVAL for hugetlb memory if the 
length is not a multiple of the underlying page size.

Documentation/vm/hugetlbpage.txt was updated to specify this behavior 
since Linux 4.1 in commit 80d6b94bd69a ("mm, doc: cleanup and clarify 
munmap behavior for hugetlb memory").

Signed-off-by: David Rientjes <rientjes@google.com>
---
 man2/mmap.2 | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/man2/mmap.2 b/man2/mmap.2
--- a/man2/mmap.2
+++ b/man2/mmap.2
@@ -383,6 +383,10 @@ All pages containing a part
 of the indicated range are unmapped, and subsequent references
 to these pages will generate
 .BR SIGSEGV .
+An exception is when the underlying memory is not of the native page
+size, such as hugetlb page sizes, whereas
+.I length
+must be a multiple of the underlying page size.
 It is not an error if the
 indicated range does not contain any mapped pages.
 .SS Timestamps changes for file-backed mappings

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