mmalloc/mvalloc.c
mmalloc/sbrk-sup.c
mmalloc/TODO
-test_ancient.ml
-test_ancient_shared.ml
-test_ancient_weblogs.ml
+README.txt
+test_ancient_dict_read.ml
+test_ancient_dict_verify.ml
+test_ancient_dict_write.ml
'Ancient' module for OCaml
----------------------------------------------------------------------
-$Id: README.txt,v 1.1 2006-10-06 15:03:47 rich Exp $
+$Id: README.txt,v 1.2 2006-10-09 12:18:05 rich Exp $
What does this module do?
----------------------------------------------------------------------
have shown that this could make a huge difference to performance, but
we are not sure how to implement this cleanly in the current library.
+(7) [Advanced topic] Certain techniques such as Address Space
+Randomisation (http://lwn.net/Articles/121845/) are probably not
+compatible with the Ancient module and shared files. Because the
+ancient data structures contain real pointers, these pointers would be
+invalidated if the shared file was not mapped in at precisely the same
+base address in all processes which are sharing the file.
+
+One solution might be to use private mappings and a list of fixups.
+In fact, the code actually builds a list of fixups currently while
+marking, because it needs to deal with precisely this issue (during
+marking, memory is allocated with realloc which might move the memory
+segment, thus real pointers cannot be stored while marking, but need
+to be fixed up afterwards). The list of fixups would need to be
+stored alongside the memory segment (currently it is discarded after
+marking), and the file would need to be mapped in using MAP_PRIVATE
+(see below).
+
+A possible problem with this is that because OCaml objects tend to be
+small and contain a lot of pointers, it is likely that fixing up the
+pointers would result in every page in the memory segment becoming
+dirty, which would basically cancel out any benefit of using shared
+mappings in the first place. However it is likely that some users of
+this module have large amounts of opaque data and few pointers, and
+for them this would be worthwhile.
+
+(8) Currently mmalloc is implemented so that the file is mapped in
+PROT_READ|PROT_WRITE and MAP_SHARED. Ancient data structures are
+supposed to be immutable so strictly speaking write access shouldn't
+be required. It may be worthwhile modifying mmalloc to allow
+read-only mappings, and private mappings.
+
+(9) The library assumes that every OCaml object is at least one word
+long. This seemed like a good assumption up until I found that
+zero-length arrays are valid zero word objects. At the moment you
+cannot mark structures which contain zero-length arrays -- you will
+get an assert-failure in the _mark function.
+
+Possibly there are other types of OCaml structure which are zero word
+objects and also cannot be marked. I'm not sure what these will be:
+for example empty strings are stored as one word OCaml objects, so
+they are OK.
+
+The solution to this bug is non-trivial.
+
Authors
----------------------------------------------------------------------
(* Mark objects as 'ancient' so they are taken out of the OCaml heap.
- * $Id: ancient.ml,v 1.4 2006-09-28 12:40:07 rich Exp $
+ * $Id: ancient.ml,v 1.5 2006-10-09 12:18:05 rich Exp $
*)
type 'a ancient
external delete : 'a ancient -> unit = "ancient_delete"
+external is_ancient : 'a -> bool = "ancient_is_ancient"
+
type md
external attach : Unix.file_descr -> nativeint -> md = "ancient_attach"
external share : md -> int -> 'a -> 'a ancient = "ancient_share"
external get : md -> int -> 'a ancient = "ancient_get"
+
+let max_key = 1023 (* MMALLOC_KEYS-1. See mmprivate.h *)
(** Mark objects as 'ancient' so they are taken out of the OCaml heap.
- * $Id: ancient.mli,v 1.5 2006-10-06 15:03:47 rich Exp $
+ * $Id: ancient.mli,v 1.6 2006-10-09 12:18:05 rich Exp $
*)
type 'a ancient
* Forgetting to delete an ancient object results in a memory leak.
*)
+val is_ancient : 'a -> bool
+ (** [is_ancient ptr] returns true if [ptr] is an object on the ancient
+ * heap.
+ *)
+
(** {6 Shared memory mappings} *)
type md
* file. See {!Ancient.attach}, {!Ancient.detach}.
*
* More than one object can be stored in a file. They are
- * indexed using integers in the range [0..1023] (the limit
+ * indexed using integers in the range [0..max_key] (the limit
* is hard-coded in [mmalloc/mmprivate.h]). The [key] parameter
* controls which object is written/overwritten by [share].
* If you do not wish to use this feature, just pass [0]
(** [get md key] returns the object indexed by [key] in the
* attached file.
*
- * The key is in the range [0..1023] (the limit is hard-coded in
+ * The key is in the range [0..max_key] (the limit is hard-coded in
* [mmalloc/mmprivate.h]). If you do not wish to use this feature,
* just pass [0] as the key when sharing / getting.
*
*
* @raises [Not_found] if no object is associated with the key.
*)
+
+val max_key : int
/* Mark objects as 'ancient' so they are taken out of the OCaml heap.
- * $Id: ancient_c.c,v 1.7 2006-10-06 12:25:20 rich Exp $
+ * $Id: ancient_c.c,v 1.8 2006-10-09 12:18:05 rich Exp $
*/
#include <string.h>
static size_t
_mark (value obj, area *ptr, area *restore, area *fixups)
{
- char *header = Hp_val (obj);
- assert (Wosize_hp (header) > 0); // Always true? (XXX)
-
// XXX This assertion might fail if someone tries to mark an object
// which is already ancient.
assert (Is_young (obj) || Is_in_heap (obj));
+ char *header = Hp_val (obj);
+
// If we've already visited this object, just return its offset
// in the out-of-heap memory.
if (memcmp (header, &visited, sizeof visited) == 0)
return (Long_val (Field (obj, 0)));
+ // XXX Actually this fails if you try to persist a zero-length
+ // array. Needs to be fixed, but it breaks some rather important
+ // functions below.
+ assert (Wosize_hp (header) > 0);
+
// Offset where we will store this object in the out-of-heap memory.
size_t offset = ptr->n;
}
CAMLprim value
+ancient_is_ancient (value obj)
+{
+ CAMLparam1 (obj);
+ CAMLlocal1 (v);
+
+ v = Is_young (obj) || Is_in_heap (obj) ? Val_false : Val_true;
+
+ CAMLreturn (v);
+}
+
+CAMLprim value
ancient_attach (value fdv, value baseaddrv)
{
CAMLparam2 (fdv, baseaddrv);
git.annexia.org / ocaml-ancient.git / commitdiff