docs: Mention that mtime is used for LRU cleanup

Closes #1095.

diff --git a/doc/MANUAL.adoc b/doc/MANUAL.adoc
index 9df93220497cde833c1418d33e7422e735da5a63..3dde53f90a539f676d30cf04c6d6f03ece7d25e0 100644 (file)
--- a/doc/MANUAL.adoc
+++ b/doc/MANUAL.adoc
@@ -1220,6 +1220,10 @@ The reason for removing more files than just those needed to not exceed the max
 limits is that a cleanup is a fairly slow operation, so it would not be a good
 idea to trigger it often, like after each cache miss.
 
+The LRU cleanup makes use of the file modification time (mtime) of cache
+entries; ccache updates mtime of the cache entries read on a cache hit to mark
+them as "recently used".
+
 
 === Manual cleanup