dlm: drop dlm_scand kthread and use timers

Currently the scand kthread acts like a garbage collection for expired
rsbs on toss list, to clean them up after a certain timeout. It triggers
every couple of seconds and iterates over the toss list while holding
ls_rsbtbl_lock for the whole hash bucket iteration.

To reduce the amount of time holding ls_rsbtbl_lock, we now handle the
disposal of expired rsbs using a per-lockspace timer that expires for the
earliest tossed rsb on the lockspace toss queue. This toss queue is
ordered according to the rsb res_toss_time with the earliest tossed rsb
as the first entry. The toss timer will only trylock() necessary locks,
since it is low priority garbage collection, and will rearm the timer
if trylock() fails. If the timer function does not find any expired
rsb's, it rearms the timer with the next earliest expired rsb.

Signed-off-by: Alexander Aring <[email protected]>
Signed-off-by: David Teigland <[email protected]>

Author: Alexander Aring

fs/dlm/dlm_internal.h

@@ -334,6 +334,7 @@ struct dlm_rsb {
 	struct list_head	res_root_list;	    /* used for recovery */
 	struct list_head	res_masters_list;   /* used for recovery */
 	struct list_head	res_recover_list;   /* used for recovery */
+	struct list_head	res_toss_q_list;
 	int			res_recover_locks_count;
 
 	char			*res_lvbptr;
@@ -584,13 +585,20 @@ struct dlm_ls {
 	spinlock_t		ls_lkbidr_spin;
 
 	struct rhashtable	ls_rsbtbl;
-#define DLM_RTF_SHRINK_BIT	0
-	unsigned long		ls_rsbtbl_flags;
 	spinlock_t		ls_rsbtbl_lock;
 
 	struct list_head	ls_toss;
 	struct list_head	ls_keep;
 
+	struct timer_list	ls_timer;
+	/* this queue is ordered according the
+	 * absolute res_toss_time jiffies time
+	 * to mod_timer() with the first element
+	 * if necessary.
+	 */
+	struct list_head	ls_toss_q;
+	spinlock_t		ls_toss_q_lock;
+
 	spinlock_t		ls_waiters_lock;
 	struct list_head	ls_waiters;	/* lkbs needing a reply */
 
@@ -601,9 +609,6 @@ struct dlm_ls {
 	int			ls_new_rsb_count;
 	struct list_head	ls_new_rsb;	/* new rsb structs */
 
-	char			*ls_remove_names[DLM_REMOVE_NAMES_MAX];
-	int			ls_remove_lens[DLM_REMOVE_NAMES_MAX];
-
 	struct list_head	ls_nodes;	/* current nodes in ls */
 	struct list_head	ls_nodes_gone;	/* dead node list, recovery */
 	int			ls_num_nodes;	/* number of nodes in ls */
@@ -640,7 +645,6 @@ struct dlm_ls {
 
 	spinlock_t		ls_cb_lock;
 	struct list_head	ls_cb_delay; /* save for queue_work later */
-	struct timer_list	ls_timer;
 	struct task_struct	*ls_recoverd_task;
 	struct mutex		ls_recoverd_active;
 	spinlock_t		ls_recover_lock;