doc: document that NEARFULL conditions can result in slow writes

The change to doing sync I/Os when we're in NEARFULL conditions
apparently caught some folks by surprise. Add something to clarify that
to the kclient debugging docs.

Also, remove the incomplete sentence that follows it, which contains no
useful information.

Fixes: https://tracker.ceph.com/issues/49406
Signed-off-by: Jeff Layton <jlayton@redhat.com>

diff --git a/doc/cephfs/troubleshooting.rst b/doc/cephfs/troubleshooting.rst
index 78ad18ddeb4d153de08a8dbe0d33874d0eefe4b7..ea33019f04367a6402d2358eabac1092b5b75c5d 100644 (file)
--- a/doc/cephfs/troubleshooting.rst
+++ b/doc/cephfs/troubleshooting.rst
@@ -124,8 +124,8 @@ slow requests are probably the ``mdsc`` and ``osdc`` files.
 * osdc: Dumps the current ops in-flight to OSDs (ie, file data IO)
 * osdmap: Dumps the current OSDMap epoch, pools, and OSDs
 
-If there are no stuck requests but you have file IO which is not progressing,
-you might have a...
+If the data pool is in a NEARFULL condition, then the kernel cephfs client
+will switch to doing writes synchronously, which is quite slow.
 
 Disconnected+Remounted FS
 =========================