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authorNeilBrown <neilb@suse.de>2007-05-11 01:23:31 -0400
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-05-11 11:29:37 -0400
commit435b71be20f2ad3688acd94c05e968e029464d60 (patch)
treefdc4b08074f148298cecd6915c6427353652b0ba /drivers/md
parent11fe250d89cdce3d6bb43bd674f3dcdcaa78dbc8 (diff)
md: improve the is_mddev_idle test
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@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'drivers/md')
-rw-r--r--drivers/md/md.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 65814b0340cb..c10ce91b64e9 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -5103,7 +5103,7 @@ static int is_mddev_idle(mddev_t *mddev)
5103 * 5103 *
5104 * Note: the following is an unsigned comparison. 5104 * Note: the following is an unsigned comparison.
5105 */ 5105 */
5106 if ((curr_events - rdev->last_events + 4096) > 8192) { 5106 if ((long)curr_events - (long)rdev->last_events > 4096) {
5107 rdev->last_events = curr_events; 5107 rdev->last_events = curr_events;
5108 idle = 0; 5108 idle = 0;
5109 } 5109 }