docs: admin-guide: cgroup-v1: update description of inactive_file

MADV_FREE pages have been moved into the LRU_INACTIVE_FILE list by commit
f7ad2a6 ("mm: move MADV_FREE pages into LRU_INACTIVE_FILE list").

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Jian Wen <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: wenjianhn

Documentation/admin-guide/cgroup-v1/memory.rst

@@ -543,7 +543,8 @@ inactive_anon	# of bytes of anonymous and swap cache memory on inactive
 		LRU list.
 active_anon	# of bytes of anonymous and swap cache memory on active
 		LRU list.
-inactive_file	# of bytes of file-backed memory on inactive LRU list.
+inactive_file	# of bytes of file-backed memory and MADV_FREE anonymous memory(
+                LazyFree pages) on inactive LRU list.
 active_file	# of bytes of file-backed memory on active LRU list.
 unevictable	# of bytes of memory that cannot be reclaimed (mlocked etc).
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