During a 'resync' or similar activity, md checks if the devices in the
array are otherwise active and winds back resync activity when they
are. This test in done in is_mddev_idle, and it is somewhat fragile -
it sometimes thinks there is non-sync io when there isn't.
The test compares the total sectors of io (disk_stat_read) with the sectors
of resync io (disk->sync_io).
This has problems because total sectors gets updated when a request completes,
while resync io gets updated when the request is submitted. The time difference
can cause large differenced between the two which do not actually imply
non-resync activity. The test currently allows for some fuzz (+/- 4096)
but there are some cases when it is not enough.
The test currently looks for any (non-fuzz) difference, either
positive or negative. This clearly is not needed. Any non-sync
activity will cause the total sectors to grow faster than the sync_io
count (never slower) so we only need to look for a positive differences.
If we do this then the amount of in-flight sync io will never cause
the appearance of non-sync IO. Once enough non-sync IO to worry about
starts happening, resync will be slowed down and the measurements will
thus be more precise (as there is less in-flight) and control of resync
will still be suitably responsive.
Signed-off-by: Neil Brown <neilb@xxxxxxx>
### Diffstat output
./drivers/md/md.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff .prev/drivers/md/md.c ./drivers/md/md.c
--- .prev/drivers/md/md.c 2007-05-10 15:51:54.000000000 +1000
+++ ./drivers/md/md.c 2007-05-10 16:05:10.000000000 +1000
@@ -5095,7 +5095,7 @@ static int is_mddev_idle(mddev_t *mddev)
*
* Note: the following is an unsigned comparison.
*/
- if ((curr_events - rdev->last_events + 4096) > 8192) {
+ if ((long)curr_events - (long)rdev->last_events > 4096) {
rdev->last_events = curr_events;
idle = 0;
}
-
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