From: Zac Dover Date: Mon, 12 Aug 2024 12:47:08 +0000 (+1000) Subject: doc/cephfs: improve cache-configuration.rst X-Git-Tag: v20.0.0~1273^2 X-Git-Url: http://git.apps.os.sepia.ceph.com/?a=commitdiff_plain;h=aa3bdae2314fef2fca8fc12dca006af657235e17;p=ceph.git doc/cephfs: improve cache-configuration.rst Improve the text in the section about dealing with cache-pressure alerts that was added in https://github.com/ceph/ceph/pull/59077. The changes in this commit were suggested by Anthony D'Atri. Co-authored-by: Patrick Donnelly Co-authored-by: Anthony D'Atri Signed-off-by: Zac Dover --- diff --git a/doc/cephfs/cache-configuration.rst b/doc/cephfs/cache-configuration.rst index 9309844f2d892..ecdedea1d6d79 100644 --- a/doc/cephfs/cache-configuration.rst +++ b/doc/cephfs/cache-configuration.rst @@ -237,12 +237,11 @@ all cached caps (the actual recall value is ``num_caps - mds_min_caps_per_client(100)``). Under certain circumstances, many "recall caps" requests can be sent so quickly -that the "mon warning limit" exceeded, and the "clients failing to respond to -cache pressure" message can be triggered. If the client does not release the -caps fast enough, the MDS repeats the "recall caps" request one second later. -This means that the MDS will send "recall caps" again and again. The "total" -counter of "recall caps" for the session will grow and grow, and will -eventually exceed the "mon warning limit". +that the health warning is generated: "clients failing to respond to cache +pressure". If the client does not release the caps fast enough, the MDS repeats +the "recall caps" request one second later. This means that the MDS will send +"recall caps" again and again. The "total" counter of "recall caps" for the +session will grow and grow, and will eventually exceed the "mon warning limit". A throttling mechanism, controlled by the ``mds_recall_max_decay_threshold`` parameter (126K by default), is available for reducing the rate of "recall @@ -258,7 +257,7 @@ Example Scenario Here is an example. A client is having 20k caps cached. At some moment the server decides the client is inactive (because the session's ``cache_liveness`` value is low). It starts to ask the client to release caps down to -``mds_min_caps_per_client`` value (100 by default). For this every seconds it +``mds_min_caps_per_client`` value (100 by default). Every second, it sends recall_caps asking to release ``caps_num - mds_min_caps_per_client`` caps (but not more than ``mds_recall_max_caps``, which is 30k by default). A client is starting to release, but is releasing with a rate of (for example) only 100