On 02/29/2012 12:53 PM, Yehuda Sadeh Weinraub wrote:
On Tue, Feb 28, 2012 at 7:40 PM, Alex Elder<elder@xxxxxxxxxxxxx> wrote:
It used to be that selecting a new unique identifier for an added
rbd device required searching all existing ones to find the highest
id is used. A recent change made that unnecessary, but made it
so that id's used were monotonically non-decreasing. It's a bit
more pleasant to have smaller rbd id's though, and this change
makes ids get allocated as they were before--each new id is one more
than the maximum currently in use.
Oh, so ignore my previous comment, though in any case we can still
exhaust the 31 bits:
loop through:
add A
add B
remove A
add C
remove B
add A
remove C
add B
OK with me. I didn't change the previous behavior.
But I'm fine with making it 64 bits. I will implement
that and post an update.
-Alex
etc..
Signed-off-by: Alex Elder<elder@xxxxxxxxxxxxx>
---
drivers/block/rbd.c | 40 ++++++++++++++++++++++++++++++++++------
1 files changed, 34 insertions(+), 6 deletions(-)
diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 042377b..4c5bb39 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -2171,18 +2171,46 @@ static void rbd_id_get(struct rbd_device *rbd_dev)
*/
static void rbd_id_put(struct rbd_device *rbd_dev)
{
- BUG_ON(rbd_dev->id< 1);
+ struct list_head *tmp;
+ int rbd_id = rbd_dev->id;
+ int max_id;
+
+ BUG_ON(rbd_id< 1);
spin_lock(&rbd_dev_list_lock);
list_del_init(&rbd_dev->node);
+
+ /*
+ * If the id being "put" is not the current maximum, there
+ * is nothing special we need to do.
+ */
+ if (rbd_id != atomic_read(&rbd_id_max)) {
+ spin_unlock(&rbd_dev_list_lock);
+ return;
+ }
+
+ /*
+ * We need to update the current maximum id. Search the
+ * list to find out what it is. We're more likely to find
+ * the maximum at the end, so search the list backward.
+ */
+ max_id = 0;
+ list_for_each_prev(tmp,&rbd_dev_list) {
+ struct rbd_device *rbd_dev;
+
+ rbd_dev = list_entry(tmp, struct rbd_device, node);
+ if (rbd_id> max_id)
+ max_id = rbd_id;
+ }
spin_unlock(&rbd_dev_list_lock);
So we still need to either use 64 bit counter, or think of a better
scheme to allocate ids. Maybe using some sorted data structure here?
/*
- * New id's are always one more than the current maximum.
- * If the id being "put" *is* that maximum, decrement the
- * maximum so the next one requested just reuses this one.
+ * The max id could have been updated by rbd_id_get(), in
+ * which case it now accurately reflects the new maximum.
+ * Be careful not to overwrite the maximum value in that
+ * case.
*/
- atomic_cmpxchg(&rbd_id_max, rbd_dev->id, rbd_dev->id - 1);
+ atomic_cmpxchg(&rbd_id_max, rbd_id, max_id);
}
static ssize_t rbd_add(struct bus_type *bus,
@@ -2217,7 +2245,7 @@ static ssize_t rbd_add(struct bus_type *bus,
INIT_LIST_HEAD(&rbd_dev->node);
INIT_LIST_HEAD(&rbd_dev->snaps);
- /* generate unique id: one more than highest used so far */
+ /* generate unique id: find highest unique id, add one */
rbd_id_get(rbd_dev);
/* parse add command */
--
1.7.5.4
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