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authormajianpeng <majianpeng@gmail.com>2013-11-15 14:55:02 +0800
committerNeilBrown <neilb@suse.de>2013-11-19 15:19:18 +1100
commit79ef3a8aa1cb1523cc231c9a90a278333c21f761 (patch)
treef5895697b8f2153fe8c0af2ff6b90967e7ab6cbb /drivers/md/raid1.h
parent8e005f7c0276317cfa8fcb0291a0df57f9ef832c (diff)
downloadlinux-79ef3a8aa1cb1523cc231c9a90a278333c21f761.tar.bz2
raid1: Rewrite the implementation of iobarrier.
There is an iobarrier in raid1 because of contention between normal IO and resync IO. It suspends all normal IO when resync/recovery happens. However if normal IO is out side the resync window, there is no contention. So this patch changes the barrier mechanism to only block IO that could contend with the resync that is currently happening. We partition the whole space into five parts. |---------|-----------|------------|----------------|-------| start next_resync start_next_window end_window start + RESYNC_WINDOW = next_resync next_resync + NEXT_NORMALIO_DISTANCE = start_next_window start_next_window + NEXT_NORMALIO_DISTANCE = end_window Firstly we introduce some concepts: 1 - RESYNC_WINDOW: For resync, there are 32 resync requests at most at the same time. A sync request is RESYNC_BLOCK_SIZE(64*1024). So the RESYNC_WINDOW is 32 * RESYNC_BLOCK_SIZE, that is 2MB. 2 - NEXT_NORMALIO_DISTANCE: the distance between next_resync and start_next_window. It also indicates the distance between start_next_window and end_window. It is currently 3 * RESYNC_WINDOW_SIZE but could be tuned if this turned out not to be optimal. 3 - next_resync: the next sector at which we will do sync IO. 4 - start: a position which is at most RESYNC_WINDOW before next_resync. 5 - start_next_window: a position which is NEXT_NORMALIO_DISTANCE beyond next_resync. Normal-io after this position doesn't need to wait for resync-io to complete. 6 - end_window: a position which is 2 * NEXT_NORMALIO_DISTANCE beyond next_resync. This also doesn't need to wait, but is counted differently. 7 - current_window_requests: the count of normalIO between start_next_window and end_window. 8 - next_window_requests: the count of normalIO after end_window. NormalIO will be partitioned into four types: NormIO1: the end sector of bio is smaller or equal the start NormIO2: the start sector of bio larger or equal to end_window NormIO3: the start sector of bio larger or equal to start_next_window. NormIO4: the location between start_next_window and end_window |--------|-----------|--------------------|----------------|-------------| | start | next_resync | start_next_window | end_window | NormIO1 NormIO4 NormIO4 NormIO3 NormIO2 For NormIO1, we don't need any io barrier. For NormIO4, we used a similar approach to the original iobarrier mechanism. The normalIO and resyncIO must be kept separate. For NormIO2/3, we add two fields to struct r1conf: "current_window_requests" and "next_window_requests". They indicate the count of active requests in the two window. For these, we don't wait for resync io to complete. For resync action, if there are NormIO4s, we must wait for it. If not, we can proceed. But if resync action reaches start_next_window and current_window_requests > 0 (that is there are NormIO3s), we must wait until the current_window_requests becomes zero. When current_window_requests becomes zero, start_next_window also moves forward. Then current_window_requests will replaced by next_window_requests. There is a problem which when and how to change from NormIO2 to NormIO3. Only then can sync action progress. We add a field in struct r1conf "start_next_window". A: if start_next_window == MaxSector, it means there are no NormIO2/3. So start_next_window = next_resync + NEXT_NORMALIO_DISTANCE B: if current_window_requests == 0 && next_window_requests != 0, it means start_next_window move to end_window There is another problem which how to differentiate between old NormIO2(now it is NormIO3) and NormIO2. For example, there are many bios which are NormIO2 and a bio which is NormIO3. NormIO3 firstly completed, so the bios of NormIO2 became NormIO3. We add a field in struct r1bio "start_next_window". This is used to record the position conf->start_next_window when the call to wait_barrier() is made in make_request(). In allow_barrier(), we check the conf->start_next_window. If r1bio->stat_next_window == conf->start_next_window, it means there is no transition between NormIO2 and NormIO3. If r1bio->start_next_window != conf->start_next_window, it mean there was a transition between NormIO2 and NormIO3. There can only have been one transition. So it only means the bio is old NormIO2. For one bio, there may be many r1bio's. So we make sure all the r1bio->start_next_window are the same value. If we met blocked_dev in make_request(), it must call allow_barrier and wait_barrier. So the former and the later value of conf->start_next_window will be change. If there are many r1bio's with differnet start_next_window, for the relevant bio, it depend on the last value of r1bio. It will cause error. To avoid this, we must wait for previous r1bios to complete. Signed-off-by: Jianpeng Ma <majianpeng@gmail.com> Signed-off-by: NeilBrown <neilb@suse.de>
Diffstat (limited to 'drivers/md/raid1.h')
-rw-r--r--drivers/md/raid1.h14
1 files changed, 14 insertions, 0 deletions
diff --git a/drivers/md/raid1.h b/drivers/md/raid1.h
index 331a98a231b4..9bebca7bff2f 100644
--- a/drivers/md/raid1.h
+++ b/drivers/md/raid1.h
@@ -41,6 +41,19 @@ struct r1conf {
*/
sector_t next_resync;
+ /* When raid1 starts resync, we divide array into four partitions
+ * |---------|--------------|---------------------|-------------|
+ * next_resync start_next_window end_window
+ * start_next_window = next_resync + NEXT_NORMALIO_DISTANCE
+ * end_window = start_next_window + NEXT_NORMALIO_DISTANCE
+ * current_window_requests means the count of normalIO between
+ * start_next_window and end_window.
+ * next_window_requests means the count of normalIO after end_window.
+ * */
+ sector_t start_next_window;
+ int current_window_requests;
+ int next_window_requests;
+
spinlock_t device_lock;
/* list of 'struct r1bio' that need to be processed by raid1d,
@@ -112,6 +125,7 @@ struct r1bio {
* in this BehindIO request
*/
sector_t sector;
+ sector_t start_next_window;
int sectors;
unsigned long state;
struct mddev *mddev;