doc: add explanatory note about cache trim rate setting

Fixes: https://tracker.ceph.com/issues/48585
Signed-off-by: Jan Fajerski <jfajerski@suse.com>

diff --git a/doc/cephfs/cache-configuration.rst b/doc/cephfs/cache-configuration.rst
index 94c970ee3960d5099e11ac3e104558d2420b0b14..e97432f4f88456553eeb30d23b99f5faaa4e3854 100644 (file)
--- a/doc/cephfs/cache-configuration.rst
+++ b/doc/cephfs/cache-configuration.rst
@@ -77,6 +77,11 @@ life for the counter. If the MDS is continually removing items from its cache,
 it will reach a steady state of ``-ln(0.5)/rate*threshold`` items removed per
 second.
 
+.. note:: Increasing the value of the confguration setting
+          ``mds_cache_trim_decay_rate`` leads to the MDS spending less time
+          trimming the cache. To increase the cache trimming rate, set a lower
+          value.
+
 The defaults are conservative and may need to be changed for production MDS with
 large cache sizes.