[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [PATCH v4 1/4] tools/ocaml/xenstored: replace hand rolled GC with weak GC references
The code here is attempting to reduce memory usage by sharing common substrings in the tree: it replaces strings with ints, and keeps a string->int map that gets manually garbage collected using a hand-rolled mark and sweep algorithm. This is unnecessary: OCaml already has a mark-and-sweep Garbage Collector runtime, and sharing of common strings in tree nodes can be achieved through Weak references: if the string hasn't been seen yet it gets added to the Weak reference table, and if it has we use the entry from the table instead, thus storing a string only once. When the string is no longer referenced OCaml's GC will drop it from the weak table: there is no need to manually do a mark-and-sweep, or to tell OCaml when to drop it. Signed-off-by: Edwin Török <edvin.torok@xxxxxxxxxx> Acked-by: Christian Lindig <christian.lindig@xxxxxxxxxx> --- Changed since V3: * repost after XSA to avoid conflicts --- tools/ocaml/xenstored/connection.ml | 3 -- tools/ocaml/xenstored/history.ml | 14 ------ tools/ocaml/xenstored/store.ml | 11 ++--- tools/ocaml/xenstored/symbol.ml | 68 ++++++----------------------- tools/ocaml/xenstored/symbol.mli | 21 ++------- tools/ocaml/xenstored/xenstored.ml | 16 +------ 6 files changed, 24 insertions(+), 109 deletions(-) diff --git a/tools/ocaml/xenstored/connection.ml b/tools/ocaml/xenstored/connection.ml index 1cf24beafd..51041dde8e 100644 --- a/tools/ocaml/xenstored/connection.ml +++ b/tools/ocaml/xenstored/connection.ml @@ -334,9 +334,6 @@ let has_more_work con = let incr_ops con = con.stat_nb_ops <- con.stat_nb_ops + 1 -let mark_symbols con = - Hashtbl.iter (fun _ t -> Store.mark_symbols (Transaction.get_store t)) con.transactions - let stats con = Hashtbl.length con.watches, con.stat_nb_ops diff --git a/tools/ocaml/xenstored/history.ml b/tools/ocaml/xenstored/history.ml index 3899353da8..ba5c9cb571 100644 --- a/tools/ocaml/xenstored/history.ml +++ b/tools/ocaml/xenstored/history.ml @@ -22,20 +22,6 @@ type history_record = { let history : history_record list ref = ref [] -(* Called from periodic_ops to ensure we don't discard symbols that are still needed. *) -(* There is scope for optimisation here, since in consecutive commits one commit's `after` - * is the same thing as the next commit's `before`, but not all commits in history are - * consecutive. *) -let mark_symbols () = - (* There are gaps where dom0's commits are missing. Otherwise we could assume that - * each element's `before` is the same thing as the next element's `after` - * since the next element is the previous commit *) - List.iter (fun hist_rec -> - Store.mark_symbols hist_rec.before; - Store.mark_symbols hist_rec.after; - ) - !history - (* 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. *) diff --git a/tools/ocaml/xenstored/store.ml b/tools/ocaml/xenstored/store.ml index a3be2e6bbe..9c226e4ef7 100644 --- a/tools/ocaml/xenstored/store.ml +++ b/tools/ocaml/xenstored/store.ml @@ -46,18 +46,18 @@ let add_child node child = let exists node childname = let childname = Symbol.of_string childname in - List.exists (fun n -> n.name = childname) node.children + List.exists (fun n -> Symbol.equal n.name childname) node.children let find node childname = let childname = Symbol.of_string childname in - List.find (fun n -> n.name = childname) node.children + List.find (fun n -> Symbol.equal n.name childname) node.children let replace_child node child nchild = (* this is the on-steroid version of the filter one-replace one *) let rec replace_one_in_list l = match l with | [] -> [] - | h :: tl when h.name = child.name -> nchild :: tl + | h :: tl when Symbol.equal h.name child.name -> nchild :: tl | h :: tl -> h :: replace_one_in_list tl in { node with children = (replace_one_in_list node.children) } @@ -67,7 +67,7 @@ let del_childname node childname = let rec delete_one_in_list l = match l with | [] -> raise Not_found - | h :: tl when h.name = sym -> tl + | h :: tl when Symbol.equal h.name sym -> tl | h :: tl -> h :: delete_one_in_list tl in { node with children = (delete_one_in_list node.children) } @@ -489,9 +489,6 @@ let copy store = { quota = Quota.copy store.quota; } -let mark_symbols store = - Node.recurse (fun node -> Symbol.mark_as_used node.Node.name) store.root - let incr_transaction_coalesce store = store.stat_transaction_coalesce <- store.stat_transaction_coalesce + 1 let incr_transaction_abort store = diff --git a/tools/ocaml/xenstored/symbol.ml b/tools/ocaml/xenstored/symbol.ml index 4420c6a4d7..2b41d120f6 100644 --- a/tools/ocaml/xenstored/symbol.ml +++ b/tools/ocaml/xenstored/symbol.ml @@ -14,63 +14,23 @@ * GNU Lesser General Public License for more details. *) -type t = int +module WeakTable = Weak.Make(struct + type t = string + let equal (x:string) (y:string) = (x = y) + let hash = Hashtbl.hash +end) -type 'a record = { data: 'a; mutable garbage: bool } -let int_string_tbl : (int,string record) Hashtbl.t = Hashtbl.create 1024 -let string_int_tbl : (string,int) Hashtbl.t = Hashtbl.create 1024 +type t = string -let created_counter = ref 0 -let used_counter = ref 0 +let tbl = WeakTable.create 1024 -let count = ref 0 -let rec fresh () = - if Hashtbl.mem int_string_tbl !count - then begin - incr count; - fresh () - end else - !count +let of_string s = WeakTable.merge tbl s +let to_string s = s -let new_record v = { data=v; garbage=false } - -let of_string name = - if Hashtbl.mem string_int_tbl name - then begin - incr used_counter; - Hashtbl.find string_int_tbl name - end else begin - let i = fresh () in - incr created_counter; - Hashtbl.add string_int_tbl name i; - Hashtbl.add int_string_tbl i (new_record name); - i - end - -let to_string i = - (Hashtbl.find int_string_tbl i).data - -let mark_all_as_unused () = - Hashtbl.iter (fun _ v -> v.garbage <- true) int_string_tbl - -let mark_as_used symb = - let record1 = Hashtbl.find int_string_tbl symb in - record1.garbage <- false - -let garbage () = - let records = Hashtbl.fold (fun symb record accu -> - if record.garbage then (symb, record.data) :: accu else accu - ) int_string_tbl [] in - let remove (int,string) = - Hashtbl.remove int_string_tbl int; - Hashtbl.remove string_int_tbl string - in - created_counter := 0; - used_counter := 0; - List.iter remove records +let equal a b = + (* compare using physical equality, both members have to be part of the above weak table *) + a == b let stats () = - Hashtbl.length string_int_tbl - -let created () = !created_counter -let used () = !used_counter + let len, entries, _, _, _, _ = WeakTable.stats tbl in + len, entries diff --git a/tools/ocaml/xenstored/symbol.mli b/tools/ocaml/xenstored/symbol.mli index c3c9f6e2f8..586ab57507 100644 --- a/tools/ocaml/xenstored/symbol.mli +++ b/tools/ocaml/xenstored/symbol.mli @@ -29,24 +29,11 @@ val of_string : string -> t val to_string : t -> string (** Convert a symbol into a string. *) -(** {6 Garbage Collection} *) - -(** Symbols need to be regulary garbage collected. The following steps should be followed: -- mark all the knowns symbols as unused (with [mark_all_as_unused]); -- mark all the symbols really usefull as used (with [mark_as_used]); and -- finally, call [garbage] *) - -val mark_all_as_unused : unit -> unit -val mark_as_used : t -> unit -val garbage : unit -> unit +val equal: t -> t -> bool +(** Compare two symbols for equality *) (** {6 Statistics } *) -val stats : unit -> int -(** Get the number of used symbols. *) +val stats : unit -> int * int +(** Get the table size and number of entries. *) -val created : unit -> int -(** Returns the number of symbols created since the last GC. *) - -val used : unit -> int -(** Returns the number of existing symbols used since the last GC *) diff --git a/tools/ocaml/xenstored/xenstored.ml b/tools/ocaml/xenstored/xenstored.ml index 5893af2caa..885b397d71 100644 --- a/tools/ocaml/xenstored/xenstored.ml +++ b/tools/ocaml/xenstored/xenstored.ml @@ -431,18 +431,6 @@ let _ = let periodic_ops now = debug "periodic_ops starting"; - (* we garbage collect the string->int dictionary after a sizeable amount of operations, - * there's no need to be really fast even if we got loose - * objects since names are often reuse. - *) - if Symbol.created () > 1000 || Symbol.used () > 20000 - then begin - Symbol.mark_all_as_unused (); - Store.mark_symbols store; - Connections.iter cons Connection.mark_symbols; - History.mark_symbols (); - Symbol.garbage () - end; (* scan all the xs rings as a safenet for ill-behaved clients *) if !ring_scan_interval >= 0 && now > (!last_scan_time +. float !ring_scan_interval) then @@ -460,11 +448,11 @@ let _ = let (lanon, lanon_ops, lanon_watchs, ldom, ldom_ops, ldom_watchs) = Connections.stats cons in let store_nodes, store_abort, store_coalesce = Store.stats store in - let symtbl_len = Symbol.stats () in + let symtbl_len, symtbl_entries = Symbol.stats () in info "store stat: nodes(%d) t-abort(%d) t-coalesce(%d)" store_nodes store_abort store_coalesce; - info "sytbl stat: %d" symtbl_len; + info "sytbl stat: length(%d) entries(%d)" symtbl_len symtbl_entries; info " con stat: anonymous(%d, %d o, %d w) domains(%d, %d o, %d w)" lanon lanon_ops lanon_watchs ldom ldom_ops ldom_watchs; info " mem stat: minor(%.0f) promoted(%.0f) major(%.0f) heap(%d w, %d c) live(%d w, %d b) free(%d w, %d b)" -- 2.29.2
|
Lists.xenproject.org is hosted with RackSpace, monitoring our |