Commit 5d05e54a authored Mar 20, 2015 by Jeff Layton Committed by Trond Myklebust Apr 23, 2015

nfs: fix high load average due to callback thread sleeping



Chuck pointed out a problem that crept in with commit 6ffa30d3 (nfs:
don't call blocking operations while !TASK_RUNNING). Linux counts tasks
in uninterruptible sleep against the load average, so this caused the
system's load average to be pinned at at least 1 when there was a
NFSv4.1+ mount active.

Not a huge problem, but it's probably worth fixing before we get too
many complaints about it. This patch converts the code back to use
TASK_INTERRUPTIBLE sleep, simply has it flush any signals on each loop
iteration. In practice no one should really be signalling this thread at
all, so I think this is reasonably safe.

With this change, there's also no need to game the hung task watchdog so
we can also convert the schedule_timeout call back to a normal schedule.

Cc: <stable@vger.kernel.org>
Reported-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
Tested-by: Chuck Lever <chuck.lever@oracle.com>
Fixes: commit 6ffa30d3 (“nfs: don't call blocking . . .”)
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

parent f830f7dd

fs/nfs/callback.c

+3 −3

Original line number	Diff line number	Diff line
		@@ -128,7 +128,7 @@ nfs41_callback_svc(void *vrqstp)
		if (try_to_freeze())
		continue;

		prepare_to_wait(&serv->sv_cb_waitq, &wq, TASK_UNINTERRUPTIBLE);
		prepare_to_wait(&serv->sv_cb_waitq, &wq, TASK_INTERRUPTIBLE);
		spin_lock_bh(&serv->sv_cb_lock);
		if (!list_empty(&serv->sv_cb_list)) {
		req = list_first_entry(&serv->sv_cb_list,
		@@ -142,10 +142,10 @@ nfs41_callback_svc(void *vrqstp)
		error);
		} else {
		spin_unlock_bh(&serv->sv_cb_lock);
		/* schedule_timeout to game the hung task watchdog */
		schedule_timeout(60 * HZ);
		schedule();
		finish_wait(&serv->sv_cb_waitq, &wq);
		}
		flush_signals(current);
		}
		return 0;
		}