Add documention for 'write_size' huge option, as well as making previous
huge options more clear.

Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
---
 Documentation/filesystems/tmpfs.rst | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/Documentation/filesystems/tmpfs.rst b/Documentation/filesystems/tmpfs.rst
index 56a26c843dbe..be998ff47018 100644
--- a/Documentation/filesystems/tmpfs.rst
+++ b/Documentation/filesystems/tmpfs.rst
@@ -115,10 +115,11 @@ The mount options for this are:
 
 ================ ==============================================================
 huge=never       Do not allocate huge pages.  This is the default.
-huge=always      Attempt to allocate huge page every time a new page is needed.
-huge=within_size Only allocate huge page if it will be fully within i_size.
+huge=always      Attempt to allocate PMD sized huge page every time a new page is needed.
+huge=within_size Only allocate PMD sized huge page if it will be fully within i_size.
                  Also respect madvise(2) hints.
-huge=advise      Only allocate huge page if requested with madvise(2).
+huge=advise      Only allocate PMD sized huge page if requested with madvise(2).
+huge=write_size  Can allocate various sized huge page based on the write size.
 ================ ==============================================================
 
 See also Documentation/admin-guide/mm/transhuge.rst, which describes the
-- 
2.39.3