Jens Axboe wrote:
+/*
+ * kupdated() used to do this. We cannot do it from the bdi_forker_task()
+ * or we risk deadlocking on ->s_umount. The longer term solution would be
+ * to implement sync_supers_bdi() or similar and simply do it from the
+ * bdi writeback tasks individually.
+ */
+static int bdi_sync_supers(void *unused)
+{
+ set_user_nice(current, 0);
+
+ while (!kthread_should_stop()) {
+ set_current_state(TASK_INTERRUPTIBLE);
+ schedule();
+
+ /*
+ * Do this periodically, like kupdated() did before.
+ */
+ sync_supers();
+ }
+
+ return 0;
ATM we have one timer for both data and super-block synchronization.
With per-bdi write-back we have:
1. one timer for super blocks
2. many per-bdi timers for data (schedule_timeout() is essentially
using timers).
This is not nice, because each timer is an additional source of
power-savings killers. I mean, it is more power management (PM)
friendly to have less timers and disturb CPU less, make CPU wake
up from retention less frequently.
I do not challange the per-bdi idea at all, but is it possible to
think about a more PM-friendly desing and have one source of
periodic write-back, not many. I mean, could there be one timer
which periodically syncs supers and wakes up the BDI write-back
tasks?
I've just started looking at your work, so I do not have good overall
picture of what's going on, so apologies in advance if I missed
something.
--
Best Regards,
Artem Bityutskiy (Артём Битюцкий)
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