oxenstored: trim history in the frequent_ops function

We were trimming the history of commits only at the end of each
transaction (regardless of how it ended).

Therefore if non-transactional writes were being made but no
transactions were being ended, the history would grow
indefinitely. Now we trim the history at regular intervals.

Signed-off-by: Thomas Sanders <thomas.sanders@citrix.com>

tools/ocaml/xenstored/history.ml

@@ -39,7 +39,8 @@ let mark_symbols () =
 (* Keep only enough commit-history to protect the running transactions that we are still tracking *)
 (* There is scope for optimisation here, replacing List.filter with something more efficient,
  * probably on a different list-like structure. *)
-let trim () =
+let trim ?txn () =
+	Transaction.trim_short_running_transactions txn;
 	history := match Transaction.oldest_short_running_transaction () with
 	| None -> [] (* We have no open transaction, so no history is needed *)
 	| Some (_, txn) -> (
@@ -49,8 +50,7 @@ let trim () =
 
 let end_transaction txn con tid commit =
 	let success = Connection.end_transaction con tid commit in
-	Transaction.end_transaction txn;
-	trim ();
+	trim ~txn ();
 	success
 
 let push (x: history_record) =

tools/ocaml/xenstored/transaction.ml

@@ -106,10 +106,14 @@ let oldest_short_running_transaction () =
 		| x :: xs -> last xs
 	in last !short_running_txns
 
-let end_transaction txn =
+let trim_short_running_transactions txn =
 	let cutoff = Unix.gettimeofday () -. !Define.conflict_max_history_seconds in
+	let keep = match txn with
+		| None -> (function (start_time, _) -> start_time >= cutoff)
+		| Some t -> (function (start_time, tx) -> start_time >= cutoff && tx != t)
+	in
 	short_running_txns := List.filter
-		(function (start_time, tx) -> start_time >= cutoff && tx != txn)
+		keep
 		!short_running_txns
 
 let make ?(internal=false) id store =

tools/ocaml/xenstored/xenstored.ml

@@ -278,6 +278,7 @@ let _ =
 	 * than the periodic_ops function *)
 	let frequent_ops () =
 		if Unix.gettimeofday () > !next_frequent_ops then (
+			History.trim ();
 			Domains.incr_conflict_credit domains;
 			advance_next_frequent_ops ()
 		) in