diff --git a/clang-tools-extra/docs/clangd/Installation.rst b/clang-tools-extra/docs/clangd/Installation.rst
--- a/clang-tools-extra/docs/clangd/Installation.rst
+++ b/clang-tools-extra/docs/clangd/Installation.rst
@@ -352,20 +352,26 @@
 Creating this file by hand is a reasonable place to start if your project is
 quite simple.
 
-Project-wide Index
-==================
+Background Indexing
+===================
 
-By default clangd only has a view on symbols coming from files you are
-currently editing. You can extend this view to whole project by providing a
-project-wide index to clangd.  There are two ways to do this.
+clangd (v9) turns on the background indexing by default, which will incrementally
+build an index of your project (all files listed in the compilation database).
+The index enables code navigation features (go-to-definition, find-references)
+and global code completion.
 
-- Pass an experimental `-background-index` command line argument.  With
-  this feature enabled, clangd incrementally builds an index of projects
-  that you work on and uses the just-built index automatically.
+- the index is saved to the ``.clangd/index`` in the project root;
+- background indexing canb be disable by the ``--background-index=false`` flag;
+  if it is disabled, clangd doesn't have a global view of the whole project, it
+  only has a view on symbols coming from files you are currently editing;
 
-- Generate an index file using `clangd-indexer
+
+Build Index Manually
+====================
+
+You probably don't need this. There is a `clangd-indexer
   <https://github.com/llvm/llvm-project/blob/master/clang-tools-extra/clangd/indexer/IndexerMain.cpp>`__
-  Then you can pass generated index file to clangd using
-  `-index-file=/path/to/index_file`.  *Note that clangd-indexer isn't
+which generates an index file for your project. To use the index, pass the flag
+`-index=file=/path/to/index_file` to clangd. *Note that clangd-indexer isn't
   included alongside clangd in the Debian clang-tools package. You will
   likely have to build it from source to use this option.*