[PATCH 5/5] doc/emacs: add discussion about notmuch-show-perfomance.

[David Bremner <david@tethera.net>]

Most of the information is already in the docstrings, but hopefully
by grouping it is more discoverable.
---
 doc/notmuch-emacs.rst | 41 +++++++++++++++++++++++++++++++----------
 1 file changed, 31 insertions(+), 10 deletions(-)

diff --git a/doc/notmuch-emacs.rst b/doc/notmuch-emacs.rst
index be7e324d..f1f7d6a9 100644
--- a/doc/notmuch-emacs.rst
+++ b/doc/notmuch-emacs.rst
@@ -266,7 +266,7 @@ pressing RET after positioning the cursor on a hidden part.
 ``?``
     Display full set of key bindings
 
-Display of messages can be controlled by the following variables
+Display of messages can be controlled by the following variables; see also :ref:`show-large`.
 
 :index:`notmuch-message-headers`
        |docstring::notmuch-message-headers|
@@ -277,15 +277,6 @@ Display of messages can be controlled by the following variables
 :index:`notmuch-show-header-line`
        |docstring::notmuch-show-header-line|
 
-:index:`notmuch-show-depth-limit`
-       |docstring::notmuch-show-depth-limit|
-
-:index:`notmuch-show-height-limit`
-       |docstring::notmuch-show-height-limit|
-
-:index:`notmuch-show-max-text-part-size`
-       |docstring::notmuch-show-max-text-part-size|
-
 :index:`notmuch-multipart/alternative-discouraged`
 
    Which mime types to hide by default for multipart messages.
@@ -307,6 +298,36 @@ Display of messages can be controlled by the following variables
            (t
             (list "text/html" "multipart/related")))))
 
+.. _show-large:
+
+Dealing with large messages and threads
+---------------------------------------
+
+If you are finding :ref:`notmuch-show` is annoyingly slow displaying
+large messages, you can customize
+:index:`notmuch-show-max-text-part-size`.  If you want to speed up the
+display of large threads (with or without large messages), there are
+several options.  First, you can display the same query in one of the
+other modes. :ref:`notmuch-unthreaded` is the most robust for
+extremely large queries, but :ref:`notmuch-tree` is also be faster
+than :ref:`notmuch-show` in general, since it only renders a single
+message a time. If you prefer to stay with the rendered thread
+("conversation") view of :ref:`notmuch-show`, you can customize the
+variables :index:`notmuch-show-depth-limit`,
+:index:`notmuch-show-height-limit` and
+:index:`notmuch-show-max-text-part-size` to limit the amount of
+rendering done initially. Note that these limits are implicitly
+*AND*-ed together, and combinations might have surprising effects.
+
+:index:`notmuch-show-depth-limit`
+       |docstring::notmuch-show-depth-limit|
+
+:index:`notmuch-show-height-limit`
+       |docstring::notmuch-show-height-limit|
+
+:index:`notmuch-show-max-text-part-size`
+       |docstring::notmuch-show-max-text-part-size|
+
 .. _show-copy:
 
 Copy to kill-ring
-- 
2.35.2