[dm-devel] [PATCH 5/9] rqdm core: simplify suspend code
Kiyoshi Ueda
k-ueda at ct.jp.nec.com
Fri Oct 16 05:01:10 UTC 2009
This patch simplifies suspend code of request-based dm.
(No change since the last post: http://patchwork.kernel.org/patch/40809/)
This patch is a preparation for PATCH 9, which waits for all in_flight
I/Os to complete without stopping request_queue and wants to use
dm_wait_for_completion() for it.
In case of suspend with "--nolockfs" but without "--noflush",
the semantics for bio-based dm has been changed in 2.6.30 as below:
before 2.6.30: I/Os submitted before the suspend invocation
are flushed
2.6.30 or later: I/Os submitted even before the suspend invocation
may not be flushed
(*) We had no idea whether the semantics change hurt someone.
(For details, see http://marc.info/?t=123994433400003&r=1&w=2)
But it seems no hurt since there is no complaint against 2.6.30
or later.
Since the semantics of request-based dm committed in 2.6.31-rc1
is still old one, change it to new one by this patch.
The semantics change makes the suspend code simple:
o Suspend is implemented as stopping request_queue
in request-based dm, and all I/Os are queued in the request_queue
even after suspend is invoked.
o To keep the old semantics, we need to distinguish which I/Os were
queued before/after the suspend invocation.
So a special barrier-like request called 'suspend marker' was
introduced.
o On the new semantics, we don't need to flush any I/O.
So we can remove the marker and the codes related to the marker
handling and I/O flushing.
After removing such codes, the suspend sequence is now below:
1. Flush all I/Os by lock_fs() if needed.
2. Stop dispatching any I/O by stopping the request_queue.
3. Wait for all in-flight I/Os to be completed or requeued.
Signed-off-by: Kiyoshi Ueda <k-ueda at ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura at ce.jp.nec.com>
Cc: Alasdair G Kergon <agk at redhat.com>
---
drivers/md/dm.c | 158 ++++----------------------------------------------------
1 file changed, 14 insertions(+), 144 deletions(-)
Index: 2.6.32-rc4/drivers/md/dm.c
===================================================================
--- 2.6.32-rc4.orig/drivers/md/dm.c
+++ 2.6.32-rc4/drivers/md/dm.c
@@ -178,9 +178,6 @@ struct mapped_device {
/* forced geometry settings */
struct hd_geometry geometry;
- /* marker of flush suspend for request-based dm */
- struct request suspend_rq;
-
/* For saving the address of __make_request for request based dm */
make_request_fn *saved_make_request_fn;
@@ -1469,11 +1466,6 @@ static struct request *clone_rq(struct r
return clone;
}
-static int dm_rq_flush_suspending(struct mapped_device *md)
-{
- return !md->suspend_rq.special;
-}
-
/*
* Called with the queue lock held.
*/
@@ -1482,14 +1474,6 @@ static int dm_prep_fn(struct request_que
struct mapped_device *md = q->queuedata;
struct request *clone;
- if (unlikely(rq == &md->suspend_rq)) {
- if (dm_rq_flush_suspending(md))
- return BLKPREP_OK;
- else
- /* The flush suspend was interrupted */
- return BLKPREP_KILL;
- }
-
if (unlikely(rq->special)) {
DMWARN("Already has something in rq->special.");
return BLKPREP_KILL;
@@ -1560,27 +1544,15 @@ static void dm_request_fn(struct request
struct request *rq;
/*
- * For noflush suspend, check blk_queue_stopped() to immediately
- * quit I/O dispatching.
+ * For suspend, check blk_queue_stopped() not to increment
+ * the number of in-flight I/Os after the queue is stopped
+ * in dm_suspend().
*/
while (!blk_queue_plugged(q) && !blk_queue_stopped(q)) {
rq = blk_peek_request(q);
if (!rq)
goto plug_and_out;
- if (unlikely(rq == &md->suspend_rq)) { /* Flush suspend maker */
- if (queue_in_flight(q))
- /* Not quiet yet. Wait more */
- goto plug_and_out;
-
- /* This device should be quiet now */
- __stop_queue(q);
- blk_start_request(rq);
- __blk_end_request_all(rq, 0);
- wake_up(&md->wait);
- goto out;
- }
-
ti = dm_table_find_target(map, blk_rq_pos(rq));
if (ti->type->busy && ti->type->busy(ti))
goto plug_and_out;
@@ -2112,7 +2084,7 @@ static int dm_wait_for_completion(struct
smp_mb();
if (dm_request_based(md)) {
spin_lock_irqsave(q->queue_lock, flags);
- if (!queue_in_flight(q) && blk_queue_stopped(q)) {
+ if (!queue_in_flight(q)) {
spin_unlock_irqrestore(q->queue_lock, flags);
break;
}
@@ -2245,67 +2217,6 @@ out:
return r;
}
-static void dm_rq_invalidate_suspend_marker(struct mapped_device *md)
-{
- md->suspend_rq.special = (void *)0x1;
-}
-
-static void dm_rq_abort_suspend(struct mapped_device *md, int noflush)
-{
- struct request_queue *q = md->queue;
- unsigned long flags;
-
- spin_lock_irqsave(q->queue_lock, flags);
- if (!noflush)
- dm_rq_invalidate_suspend_marker(md);
- __start_queue(q);
- spin_unlock_irqrestore(q->queue_lock, flags);
-}
-
-static void dm_rq_start_suspend(struct mapped_device *md, int noflush)
-{
- struct request *rq = &md->suspend_rq;
- struct request_queue *q = md->queue;
-
- if (noflush)
- stop_queue(q);
- else {
- blk_rq_init(q, rq);
- blk_insert_request(q, rq, 0, NULL);
- }
-}
-
-static int dm_rq_suspend_available(struct mapped_device *md, int noflush)
-{
- int r = 1;
- struct request *rq = &md->suspend_rq;
- struct request_queue *q = md->queue;
- unsigned long flags;
-
- if (noflush)
- return r;
-
- /* The marker must be protected by queue lock if it is in use */
- spin_lock_irqsave(q->queue_lock, flags);
- if (unlikely(rq->ref_count)) {
- /*
- * This can happen, when the previous flush suspend was
- * interrupted, the marker is still in the queue and
- * this flush suspend has been invoked, because we don't
- * remove the marker at the time of suspend interruption.
- * We have only one marker per mapped_device, so we can't
- * start another flush suspend while it is in use.
- */
- BUG_ON(!rq->special); /* The marker should be invalidated */
- DMWARN("Invalidating the previous flush suspend is still in"
- " progress. Please retry later.");
- r = 0;
- }
- spin_unlock_irqrestore(q->queue_lock, flags);
-
- return r;
-}
-
/*
* Functions to lock and unlock any filesystem running on the
* device.
@@ -2348,49 +2259,11 @@ static void unlock_fs(struct mapped_devi
/*
* Suspend mechanism in request-based dm.
*
- * After the suspend starts, further incoming requests are kept in
- * the request_queue and deferred.
- * Remaining requests in the request_queue at the start of suspend are flushed
- * if it is flush suspend.
- * The suspend completes when the following conditions have been satisfied,
- * so wait for it:
- * 1. q->in_flight is 0 (which means no in_flight request)
- * 2. queue has been stopped (which means no request dispatching)
- *
- *
- * Noflush suspend
- * ---------------
- * Noflush suspend doesn't need to dispatch remaining requests.
- * So stop the queue immediately. Then, wait for all in_flight requests
- * to be completed or requeued.
- *
- * To abort noflush suspend, start the queue.
+ * 1. Flush all I/Os by lock_fs() if needed.
+ * 2. Stop dispatching any I/O by stopping the request_queue.
+ * 3. Wait for all in-flight I/Os to be completed or requeued.
*
- *
- * Flush suspend
- * -------------
- * Flush suspend needs to dispatch remaining requests. So stop the queue
- * after the remaining requests are completed. (Requeued request must be also
- * re-dispatched and completed. Until then, we can't stop the queue.)
- *
- * During flushing the remaining requests, further incoming requests are also
- * inserted to the same queue. To distinguish which requests are to be
- * flushed, we insert a marker request to the queue at the time of starting
- * flush suspend, like a barrier.
- * The dispatching is blocked when the marker is found on the top of the queue.
- * And the queue is stopped when all in_flight requests are completed, since
- * that means the remaining requests are completely flushed.
- * Then, the marker is removed from the queue.
- *
- * To abort flush suspend, we also need to take care of the marker, not only
- * starting the queue.
- * We don't remove the marker forcibly from the queue since it's against
- * the block-layer manner. Instead, we put a invalidated mark on the marker.
- * When the invalidated marker is found on the top of the queue, it is
- * immediately removed from the queue, so it doesn't block dispatching.
- * Because we have only one marker per mapped_device, we can't start another
- * flush suspend until the invalidated marker is removed from the queue.
- * So fail and return with -EBUSY in such a case.
+ * To abort suspend, start the request_queue.
*/
int dm_suspend(struct mapped_device *md, unsigned suspend_flags)
{
@@ -2406,11 +2279,6 @@ int dm_suspend(struct mapped_device *md,
goto out_unlock;
}
- if (dm_request_based(md) && !dm_rq_suspend_available(md, noflush)) {
- r = -EBUSY;
- goto out_unlock;
- }
-
map = dm_get_table(md);
/*
@@ -2424,8 +2292,10 @@ int dm_suspend(struct mapped_device *md,
dm_table_presuspend_targets(map);
/*
- * Flush I/O to the device. noflush supersedes do_lockfs,
- * because lock_fs() needs to flush I/Os.
+ * Flush I/O to the device.
+ * Any I/O submitted after lock_fs() may not be flushed.
+ * noflush supersedes do_lockfs, because lock_fs() needs to flush I/Os
+ * and wait for the flushed I/Os to complete.
*/
if (!noflush && do_lockfs) {
r = lock_fs(md);
@@ -2457,7 +2327,7 @@ int dm_suspend(struct mapped_device *md,
flush_workqueue(md->wq);
if (dm_request_based(md))
- dm_rq_start_suspend(md, noflush);
+ stop_queue(md->queue);
/*
* At this point no more requests are entering target request routines.
@@ -2476,7 +2346,7 @@ int dm_suspend(struct mapped_device *md,
dm_queue_flush(md);
if (dm_request_based(md))
- dm_rq_abort_suspend(md, noflush);
+ start_queue(md->queue);
unlock_fs(md);
goto out; /* pushback list is already flushed, so skip flush */
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