From 1ddbe94eda58597cb6dd464b455cb62d3f68be7b Mon Sep 17 00:00:00 2001 From: Alex Elder Date: Sun, 29 Jan 2012 13:57:44 -0600 Subject: [PATCH] rbd: rework calculation of new rbd id's In order to select a new unique identifier for an added rbd device, the list of all existing ones is searched and a value one greater than the highest id is used. The list search can be avoided by using an atomic variable that keeps track of the current highest id. Using a get/put model for id's we can limit the boundless growth of id numbers a bit by arranging to reuse the current highest id once it gets released. Add these calls to "put" the id when an rbd is getting removed. Note that this changes the pattern of device id's used--new values will never be below the highest one seen so far (even if there exists an unused lower one). I assert this is OK because the key property of an rbd id is its uniqueness, not its magnitude. Regardless, a follow-on patch will restore the old way of doing things, I just think this commit just makes the incremental change to atomics a little easier to understand. Signed-off-by: Alex Elder Signed-off-by: Sage Weil --- drivers/block/rbd.c | 35 +++++++++++++++++++++++------------ 1 file changed, 23 insertions(+), 12 deletions(-) diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c index aaa19d8c3670..62da8ccc5fcb 100644 --- a/drivers/block/rbd.c +++ b/drivers/block/rbd.c @@ -2149,21 +2149,29 @@ static int rbd_init_watch_dev(struct rbd_device *rbd_dev) return ret; } -/* caller must hold ctl_mutex */ +static atomic64_t rbd_id_max = ATOMIC64_INIT(0); + +/* + * Get a unique rbd identifier. The minimum rbd id is 1. + */ static int rbd_id_get(void) { - struct list_head *tmp; - int new_id = 0; - - list_for_each(tmp, &rbd_dev_list) { - struct rbd_device *rbd_dev; + return atomic64_inc_return(&rbd_id_max); +} - rbd_dev = list_entry(tmp, struct rbd_device, node); - if (rbd_dev->id >= new_id) - new_id = rbd_dev->id + 1; - } +/* + * Record that an rbd identifier is no longer in use. + */ +static void rbd_id_put(int rbd_id) +{ + BUG_ON(rbd_id < 1); - return new_id; + /* + * 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. + */ + atomic64_cmpxchg(&rbd_id_max, rbd_id, rbd_id - 1); } static ssize_t rbd_add(struct bus_type *bus, @@ -2200,7 +2208,7 @@ static ssize_t rbd_add(struct bus_type *bus, init_rwsem(&rbd_dev->header.snap_rwsem); - /* generate unique id: find highest unique id, add one */ + /* generate unique id: one more than highest used so far */ mutex_lock_nested(&ctl_mutex, SINGLE_DEPTH_NESTING); rbd_dev->id = rbd_id_get(); @@ -2270,6 +2278,7 @@ err_out_bus: mutex_lock_nested(&ctl_mutex, SINGLE_DEPTH_NESTING); list_del_init(&rbd_dev->node); mutex_unlock(&ctl_mutex); + rbd_id_put(target_id); /* this will also clean up rest of rbd_dev stuff */ @@ -2286,6 +2295,7 @@ err_out_client: err_out_slot: list_del_init(&rbd_dev->node); mutex_unlock(&ctl_mutex); + rbd_id_put(target_id); kfree(rbd_dev); err_out_opt: @@ -2363,6 +2373,7 @@ static ssize_t rbd_remove(struct bus_type *bus, } list_del_init(&rbd_dev->node); + rbd_id_put(target_id); __rbd_remove_all_snaps(rbd_dev); rbd_bus_del_dev(rbd_dev); -- 2.20.1