docs: Mention that mtime is used for LRU cleanup

Closes #1095.

(cherry picked from commit b1c37b330c24fd2b9f3f41762a755a51806fbaaf)

diff --git a/doc/MANUAL.adoc b/doc/MANUAL.adoc
index 99ffa6b97d48abecee6ce903fb3784cd32a784dc..ec58e13bf18f269f68c6db285bfc7c4af17893ab 100644 (file)
--- a/doc/MANUAL.adoc
+++ b/doc/MANUAL.adoc
@@ -1213,6 +1213,10 @@ 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