doc: add docs about log's "memory level"

Signed-off-by: Kefu Chai <kchai@redhat.com>

diff --git a/doc/rados/troubleshooting/log-and-debug.rst b/doc/rados/troubleshooting/log-and-debug.rst
index 4a332a9001dd64e3c86f2dc7daddfecee1a9f1e7..0f5afd0a155ba9bc7beb5b3052848aa66e5d6636 100644 (file)
--- a/doc/rados/troubleshooting/log-and-debug.rst
+++ b/doc/rados/troubleshooting/log-and-debug.rst
@@ -147,7 +147,11 @@ Each subsystem has a logging level for its output logs, and for its logs
 in-memory. You may set different values for each of these subsystems by setting
 a log file level and a memory level for debug logging. Ceph's logging levels
 operate on a scale of ``1`` to ``20``, where ``1`` is terse and ``20`` is
-verbose. 
+verbose. In general, the logs in-memory are not sent to the output log unless:
+
+- a fatal signal is raised or
+- an ``assert`` in source code is triggered or
+- upon requested. Please consult document on admin socket for more details.
 
 A debug logging setting can take a single value for the log level and the
 memory level, which sets them both as the same value. For example, if you