dm thin: remap the bios in a cell immediately

This use of direct submission in process_prepared_mapping() reduces
latency for submitting bios in a cell by avoiding adding those bios to
the deferred list and waiting for the next iteration of the worker.

But this direct submission exposes the potential for a race between
releasing a cell and incrementing deferred set.  Fix this by introducing
dm_cell_visit_release() and refactoring inc_remap_and_issue_cell()
accordingly.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

diff --git a/drivers/md/dm-bio-prison.c b/drivers/md/dm-bio-prison.c
index 90a5662..bbe22a5 100644 (file)
--- a/drivers/md/dm-bio-prison.c
+++ b/drivers/md/dm-bio-prison.c
@@ -241,6 +241,20 @@ void dm_cell_error(struct dm_bio_prison *prison,
 }
 EXPORT_SYMBOL_GPL(dm_cell_error);
 
+void dm_cell_visit_release(struct dm_bio_prison *prison,
+                          void (*visit_fn)(void *, struct dm_bio_prison_cell *),
+                          void *context,
+                          struct dm_bio_prison_cell *cell)
+{
+       unsigned long flags;
+
+       spin_lock_irqsave(&prison->lock, flags);
+       visit_fn(context, cell);
+       rb_erase(&cell->node, &prison->cells);
+       spin_unlock_irqrestore(&prison->lock, flags);
+}
+EXPORT_SYMBOL_GPL(dm_cell_visit_release);
+
 /*----------------------------------------------------------------*/
 
 #define DEFERRED_SET_SIZE 64

diff --git a/drivers/md/dm-bio-prison.h b/drivers/md/dm-bio-prison.h
index c0cddb1..b039886 100644 (file)
--- a/drivers/md/dm-bio-prison.h
+++ b/drivers/md/dm-bio-prison.h
@@ -89,6 +89,14 @@ void dm_cell_release_no_holder(struct dm_bio_prison *prison,
 void dm_cell_error(struct dm_bio_prison *prison,
                   struct dm_bio_prison_cell *cell, int error);
 
+/*
+ * Visits the cell and then releases.  Guarantees no new inmates are
+ * inserted between the visit and release.
+ */
+void dm_cell_visit_release(struct dm_bio_prison *prison,
+                          void (*visit_fn)(void *, struct dm_bio_prison_cell *),
+                          void *context, struct dm_bio_prison_cell *cell);
+
 /*----------------------------------------------------------------*/
 
 /*

diff --cc drivers/md/dm-thin.c
Simple merge