dev-manual: how to purge duplicate sstate cache files

(From yocto-docs rev: 113400eb47c13617f08b415bc9ddb4526429049c)

Signed-off-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/dev-manual/common-tasks.rst

@@ -6240,8 +6240,11 @@ Changing the listed common targets is as easy as editing your version of
 ``conf-notes.txt`` in your custom template configuration directory and
 making sure you have ``TEMPLATECONF`` set to your directory.
 
+Conserving Disk Space
+=====================
+
 Conserving Disk Space During Builds
-===================================
+-----------------------------------
 
 To help conserve disk space during builds, you can add the following
 statement to your project's ``local.conf`` configuration file found in
@@ -6255,6 +6258,26 @@ building a recipe once the recipe is built. For more information on
 :ref:`rm_work <ref-classes-rm-work>` class in the
 Yocto Project Reference Manual.
 
+Purging Duplicate Shared State Cache Files
+-------------------------------------------
+
+After multiple build iterations, the Shared State (sstate) cache can contain
+duplicate cache files for a given package, while only the most recent one
+is likely to be reusable. The following command purges all but the
+newest sstate cache file for each package::
+
+   sstate-cache-management.sh --remove-duplicated --cache-dir=build/sstate-cache
+
+This command will ask you to confirm the deletions it identifies.
+
+Note::
+
+   The duplicated sstate cache files of one package must have the same
+   architecture, which means that sstate cache files with multiple
+   architectures are not considered as duplicate.
+
+Run ``sstate-cache-management.sh`` for more details about this script.
+
 Working with Packages
 =====================