Hi
I tried using Docker on my Fedora NAS box. It created a thin pool LV,
which caused hard drive activity every ~10 seconds.
dmeventd queries the thin pool every 10 seconds, and it causes a
transaction commit in order to make sure the statistics are up to date.
But transactions are already supposed to be committed after 1 second.
(See Documentation/device-mapper/thin-provisioning.txt, "Updating
on-disk metadata").
It seems like a simple case of "don't do that". The kernel already lets
us avoid the commit. How about it (patch below)? If it seems
reasonable, I can whip up a commit message for it.
Thanks
Alan
diff --git a/daemons/dmeventd/dmeventd.c b/daemons/dmeventd/dmeventd.c
index c093d91..5948f15 100644
--- a/daemons/dmeventd/dmeventd.c
+++ b/daemons/dmeventd/dmeventd.c
@@ -412,6 +412,15 @@ static struct thread_status *_alloc_thread_status(const struct message_data *dat
if (!(thread->device.name = dm_strdup(data->device_uuid)))
goto_out;
+ /*
+ * Avoid repeatedly forcing a flush.
+ * Allow the disks to sleep, and accept "out-of-date" statistics.
+ * E.g. affects thin pools. Commits will occur every second already,
+ * if the pool state is changing.
+ */
+ if (!dm_task_no_flush(thread->wait_task))
+ goto_out;
+
/* runs ioctl and may register lvm2 pluging */
thread->processing = 1;
thread->status = DM_THREAD_REGISTERING;
diff --git a/daemons/dmeventd/dmeventd.c b/daemons/dmeventd/dmeventd.c
index c093d91..5948f15 100644
--- a/daemons/dmeventd/dmeventd.c
+++ b/daemons/dmeventd/dmeventd.c
@@ -412,6 +412,15 @@ static struct thread_status *_alloc_thread_status(const struct message_data *dat
if (!(thread->device.name = dm_strdup(data->device_uuid)))
goto_out;
+ /*
+ * Avoid repeatedly forcing a flush.
+ * Allow the disks to sleep, and accept "out-of-date" statistics.
+ * E.g. affects thin pools. Commits will occur every second already,
+ * if the pool state is changing.
+ */
+ if (!dm_task_no_flush(thread->wait_task))
+ goto_out;
+
/* runs ioctl and may register lvm2 pluging */
thread->processing = 1;
thread->status = DM_THREAD_REGISTERING;
--
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