From: Lars Ellenberg <lars.ellenb...@linbit.com>
A request hitting an already "hot" extent should proceed right away,
even if some other requests need to wait for pending transactions.
Without that short-circuit, several simultaneous make_request contexts
race for committing the transaction, possibly penalizing the innocent.
Signed-off-by: Philipp Reisner <philipp.reis...@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenb...@linbit.com>
---
drivers/block/drbd/drbd_actlog.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
diff --git a/drivers/block/drbd/drbd_actlog.c b/drivers/block/drbd/drbd_actlog.c
index 82199d9..1d7244d 100644
--- a/drivers/block/drbd/drbd_actlog.c
+++ b/drivers/block/drbd/drbd_actlog.c
@@ -256,6 +256,7 @@ void drbd_al_begin_io(struct drbd_conf *mdev, struct
drbd_interval *i, bool dele
unsigned first = i->sector >> (AL_EXTENT_SHIFT-9);
unsigned last = i->size == 0 ? first : (i->sector + (i->size >> 9) - 1)
>> (AL_EXTENT_SHIFT-9);
unsigned enr;
+ bool need_transaction = false;
bool locked = false;
/* When called through generic_make_request(), we must delegate
@@ -273,8 +274,17 @@ void drbd_al_begin_io(struct drbd_conf *mdev, struct
drbd_interval *i, bool dele
D_ASSERT(first <= last);
D_ASSERT(atomic_read(&mdev->local_cnt) > 0);
- for (enr = first; enr <= last; enr++)
- wait_event(mdev->al_wait, _al_get(mdev, enr) != NULL);
+ for (enr = first; enr <= last; enr++) {
+ struct lc_element *al_ext;
+ wait_event(mdev->al_wait, (al_ext = _al_get(mdev, enr)) !=
NULL);
+ if (al_ext->lc_number != enr)
+ need_transaction = true;
+ }
+
+ /* If *this* request was to an already active extent,
+ * we're done, even if there are pending changes. */
+ if (!need_transaction)
+ return;
/* Serialize multiple transactions.
* This uses test_and_set_bit, memory barrier is implicit.
--
1.7.9.5
--
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