[PATCH v3 2/2] man/man2/mremap.2: describe previously undocumented shrink behaviour

There is pre-existing logic that appears to be undocumented for an mremap()
shrink operation, where it turns out that the usual 'input range must span
a single mapping' requirement no longer applies.

In fact, it turns out that the input range specified by [old_address,
old_size) may span any number of mappings, as long old_address resides at
or within a mapping and [old_address, new_size) spans only a single
mapping.

Explicitly document this.

Signed-off-by: Lorenzo Stoakes <redacted>
---
 man/man2/mremap.2 | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/man/man2/mremap.2 b/man/man2/mremap.2
index 6ba51310c..bbd807f1b 100644
--- a/man/man2/mremap.2
+++ b/man/man2/mremap.2

@@ -48,8 +48,24 @@ The
 .B MREMAP_DONTUNMAP
 flag may be specified.
 .P
-If the operation is not
-simply moving mappings,
+Equally, if the operation performs a shrink,
+that is if
+.I old_size
+is greater than
+.IR new_size ,
+then
+.I old_size
+may also span multiple mappings
+which do not have to be
+adjacent to one another.
+However in this case,
+.I new_size
+must span only a single mapping.
+.P
+If the operation is neither a
+.B MREMAP_FIXED
+move
+nor a shrink,
 then
 .I old_size
 must span only a single mapping.

-- 
2.50.1