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(**************************************************************************)
(* *)
(* OCaml *)
(* *)
(* Damien Doligez, projet Para, INRIA Rocquencourt *)
(* Jacques-Henri Jourdan, projet Gallium, INRIA Paris *)
(* *)
(* Copyright 1996-2016 Institut National de Recherche en Informatique *)
(* et en Automatique. *)
(* *)
(* All rights reserved. This file is distributed under the terms of *)
(* the GNU Lesser General Public License version 2.1, with the *)
(* special exception on linking described in the file LICENSE. *)
(* *)
(**************************************************************************)
(** Memory management control and statistics; finalised values. *)
type stat =
{ minor_words : float;
(** Number of words allocated in the minor heap since
the program was started. *)
promoted_words : float;
(** Number of words allocated in the minor heap that
survived a minor collection and were moved to the major heap
since the program was started. *)
major_words : float;
(** Number of words allocated in the major heap, including
the promoted words, since the program was started. *)
minor_collections : int;
(** Number of minor collections since the program was started. *)
major_collections : int;
(** Number of major collection cycles completed since the program
was started. *)
heap_words : int;
(** Total size of the major heap, in words. *)
heap_chunks : int;
(** Number of contiguous pieces of memory that make up the major heap. *)
live_words : int;
(** Number of words of live data in the major heap, including the header
words. *)
live_blocks : int;
(** Number of live blocks in the major heap. *)
free_words : int;
(** Number of words in the free list. *)
free_blocks : int;
(** Number of blocks in the free list. *)
largest_free : int;
(** Size (in words) of the largest block in the free list. *)
fragments : int;
(** Number of wasted words due to fragmentation. These are
1-words free blocks placed between two live blocks. They
are not available for allocation. *)
compactions : int;
(** Number of heap compactions since the program was started. *)
top_heap_words : int;
(** Maximum size reached by the major heap, in words. *)
stack_size: int;
(** Current size of the stack, in words. @since 3.12.0 *)
forced_major_collections: int;
(** Number of forced full major collections completed since the program
was started. @since 4.12.0 *)
}
(** The memory management counters are returned in a [stat] record.
The total amount of memory allocated by the program since it was started
is (in words) [minor_words + major_words - promoted_words]. Multiply by
the word size (4 on a 32-bit machine, 8 on a 64-bit machine) to get
the number of bytes.
*)
type control =
{ mutable minor_heap_size : int;
[@ocaml.deprecated_mutable "Use {(Gc.get()) with Gc.minor_heap_size = ...}"]
(** The size (in words) of the minor heap. Changing
this parameter will trigger a minor collection. Default: 256k. *)
mutable major_heap_increment : int;
[@ocaml.deprecated_mutable
"Use {(Gc.get()) with Gc.major_heap_increment = ...}"]
(** How much to add to the major heap when increasing it. If this
number is less than or equal to 1000, it is a percentage of
the current heap size (i.e. setting it to 100 will double the heap
size at each increase). If it is more than 1000, it is a fixed
number of words that will be added to the heap. Default: 15. *)
mutable space_overhead : int;
[@ocaml.deprecated_mutable "Use {(Gc.get()) with Gc.space_overhead = ...}"]
(** The major GC speed is computed from this parameter.
This is the memory that will be "wasted" because the GC does not
immediately collect unreachable blocks. It is expressed as a
percentage of the memory used for live data.
The GC will work more (use more CPU time and collect
blocks more eagerly) if [space_overhead] is smaller.
Default: 80. *)
mutable verbose : int;
[@ocaml.deprecated_mutable "Use {(Gc.get()) with Gc.verbose = ...}"]
(** This value controls the GC messages on standard error output.
It is a sum of some of the following flags, to print messages
on the corresponding events:
- [0x001] Start and end of major GC cycle.
- [0x002] Minor collection and major GC slice.
- [0x004] Growing and shrinking of the heap.
- [0x008] Resizing of stacks and memory manager tables.
- [0x010] Heap compaction.
- [0x020] Change of GC parameters.
- [0x040] Computation of major GC slice size.
- [0x080] Calling of finalisation functions.
- [0x100] Bytecode executable and shared library search at start-up.
- [0x200] Computation of compaction-triggering condition.
- [0x400] Output GC statistics at program exit.
Default: 0. *)
mutable max_overhead : int;
[@ocaml.deprecated_mutable "Use {(Gc.get()) with Gc.max_overhead = ...}"]
(** Heap compaction is triggered when the estimated amount
of "wasted" memory is more than [max_overhead] percent of the
amount of live data. If [max_overhead] is set to 0, heap
compaction is triggered at the end of each major GC cycle
(this setting is intended for testing purposes only).
If [max_overhead >= 1000000], compaction is never triggered.
If compaction is permanently disabled, it is strongly suggested
to set [allocation_policy] to 2.
Default: 500. *)
mutable stack_limit : int;
[@ocaml.deprecated_mutable "Use {(Gc.get()) with Gc.stack_limit = ...}"]
(** The maximum size of the stack (in words). This is only
relevant to the byte-code runtime, as the native code runtime
uses the operating system's stack. Default: 1024k. *)
mutable allocation_policy : int;
[@ocaml.deprecated_mutable
"Use {(Gc.get()) with Gc.allocation_policy = ...}"]
(** The policy used for allocating in the major heap.
Possible values are 0, 1 and 2.
- 0 is the next-fit policy, which is usually fast but can
result in fragmentation, increasing memory consumption.
- 1 is the first-fit policy, which avoids fragmentation but
has corner cases (in certain realistic workloads) where it
is sensibly slower.
- 2 is the best-fit policy, which is fast and avoids
fragmentation. In our experiments it is faster and uses less
memory than both next-fit and first-fit.
(since OCaml 4.10)
The current default is next-fit, as the best-fit policy is new
and not yet widely tested. We expect best-fit to become the
default in the future.
On one example that was known to be bad for next-fit and first-fit,
next-fit takes 28s using 855Mio of memory,
first-fit takes 47s using 566Mio of memory,
best-fit takes 27s using 545Mio of memory.
Note: When changing to a low-fragmentation policy, you may
need to augment the [space_overhead] setting, for example
using [100] instead of the default [80] which is tuned for
next-fit. Indeed, the difference in fragmentation behavior
means that different policies will have different proportion
of "wasted space" for a given program. Less fragmentation
means a smaller heap so, for the same amount of wasted space,
a higher proportion of wasted space. This makes the GC work
harder, unless you relax it by increasing [space_overhead].
Note: changing the allocation policy at run-time forces
a heap compaction, which is a lengthy operation unless the
heap is small (e.g. at the start of the program).
Default: 0.
@since 3.11.0 *)
window_size : int;
(** The size of the window used by the major GC for smoothing
out variations in its workload. This is an integer between
1 and 50.
Default: 1. @since 4.03.0 *)
custom_major_ratio : int;
(** Target ratio of floating garbage to major heap size for
out-of-heap memory held by custom values located in the major
heap. The GC speed is adjusted to try to use this much memory
for dead values that are not yet collected. Expressed as a
percentage of major heap size. The default value keeps the
out-of-heap floating garbage about the same size as the
in-heap overhead.
Note: this only applies to values allocated with
[caml_alloc_custom_mem] (e.g. bigarrays).
Default: 44.
@since 4.08.0 *)
custom_minor_ratio : int;
(** Bound on floating garbage for out-of-heap memory held by
custom values in the minor heap. A minor GC is triggered when
this much memory is held by custom values located in the minor
heap. Expressed as a percentage of minor heap size.
Note: this only applies to values allocated with
[caml_alloc_custom_mem] (e.g. bigarrays).
Default: 100.
@since 4.08.0 *)
custom_minor_max_size : int;
(** Maximum amount of out-of-heap memory for each custom value
allocated in the minor heap. When a custom value is allocated
on the minor heap and holds more than this many bytes, only
this value is counted against [custom_minor_ratio] and the
rest is directly counted against [custom_major_ratio].
Note: this only applies to values allocated with
[caml_alloc_custom_mem] (e.g. bigarrays).
Default: 8192 bytes.
@since 4.08.0 *)
}
(** The GC parameters are given as a [control] record. Note that
these parameters can also be initialised by setting the
OCAMLRUNPARAM environment variable. See the documentation of
[ocamlrun]. *)
external stat : unit -> stat = "caml_gc_stat"
(** Return the current values of the memory management counters in a
[stat] record. This function examines every heap block to get the
statistics. *)
external quick_stat : unit -> stat = "caml_gc_quick_stat"
(** Same as [stat] except that [live_words], [live_blocks], [free_words],
[free_blocks], [largest_free], and [fragments] are set to 0. This
function is much faster than [stat] because it does not need to go
through the heap. *)
external counters : unit -> float * float * float = "caml_gc_counters"
(** Return [(minor_words, promoted_words, major_words)]. This function
is as fast as [quick_stat]. *)
external minor_words : unit -> (float [@unboxed])
= "caml_gc_minor_words" "caml_gc_minor_words_unboxed"
(** Number of words allocated in the minor heap since the program was
started. This number is accurate in byte-code programs, but only an
approximation in programs compiled to native code.
In native code this function does not allocate.
@since 4.04 *)
external get : unit -> control = "caml_gc_get"
(** Return the current values of the GC parameters in a [control] record. *)
external set : control -> unit = "caml_gc_set"
(** [set r] changes the GC parameters according to the [control] record [r].
The normal usage is: [Gc.set { (Gc.get()) with Gc.verbose = 0x00d }] *)
external minor : unit -> unit = "caml_gc_minor"
(** Trigger a minor collection. *)
external major_slice : int -> int = "caml_gc_major_slice"
(** [major_slice n]
Do a minor collection and a slice of major collection. [n] is the
size of the slice: the GC will do enough work to free (on average)
[n] words of memory. If [n] = 0, the GC will try to do enough work
to ensure that the next automatic slice has no work to do.
This function returns an unspecified integer (currently: 0). *)
external major : unit -> unit = "caml_gc_major"
(** Do a minor collection and finish the current major collection cycle. *)
external full_major : unit -> unit = "caml_gc_full_major"
(** Do a minor collection, finish the current major collection cycle,
and perform a complete new cycle. This will collect all currently
unreachable blocks. *)
external compact : unit -> unit = "caml_gc_compaction"
(** Perform a full major collection and compact the heap. Note that heap
compaction is a lengthy operation. *)
val print_stat : out_channel -> unit
(** Print the current values of the memory management counters (in
human-readable form) into the channel argument. *)
val allocated_bytes : unit -> float
(** Return the total number of bytes allocated since the program was
started. It is returned as a [float] to avoid overflow problems
with [int] on 32-bit machines. *)
external get_minor_free : unit -> int = "caml_get_minor_free"
(** Return the current size of the free space inside the minor heap.
@since 4.03.0 *)
external get_bucket : int -> int = "caml_get_major_bucket" [@@noalloc]
(** [get_bucket n] returns the current size of the [n]-th future bucket
of the GC smoothing system. The unit is one millionth of a full GC.
@raise Invalid_argument if [n] is negative, return 0 if n is larger
than the smoothing window.
@since 4.03.0 *)
external get_credit : unit -> int = "caml_get_major_credit" [@@noalloc]
(** [get_credit ()] returns the current size of the "work done in advance"
counter of the GC smoothing system. The unit is one millionth of a
full GC.
@since 4.03.0 *)
external huge_fallback_count : unit -> int = "caml_gc_huge_fallback_count"
(** Return the number of times we tried to map huge pages and had to fall
back to small pages. This is always 0 if [OCAMLRUNPARAM] contains [H=1].
@since 4.03.0 *)
val finalise : ('a -> unit) -> 'a -> unit
(** [finalise f v] registers [f] as a finalisation function for [v].
[v] must be heap-allocated. [f] will be called with [v] as
argument at some point between the first time [v] becomes unreachable
(including through weak pointers) and the time [v] is collected by
the GC. Several functions can
be registered for the same value, or even several instances of the
same function. Each instance will be called once (or never,
if the program terminates before [v] becomes unreachable).
The GC will call the finalisation functions in the order of
deallocation. When several values become unreachable at the
same time (i.e. during the same GC cycle), the finalisation
functions will be called in the reverse order of the corresponding
calls to [finalise]. If [finalise] is called in the same order
as the values are allocated, that means each value is finalised
before the values it depends upon. Of course, this becomes
false if additional dependencies are introduced by assignments.
In the presence of multiple OCaml threads it should be assumed that
any particular finaliser may be executed in any of the threads.
Anything reachable from the closure of finalisation functions
is considered reachable, so the following code will not work
as expected:
- [ let v = ... in Gc.finalise (fun _ -> ...v...) v ]
Instead you should make sure that [v] is not in the closure of
the finalisation function by writing:
- [ let f = fun x -> ... let v = ... in Gc.finalise f v ]
The [f] function can use all features of OCaml, including
assignments that make the value reachable again. It can also
loop forever (in this case, the other
finalisation functions will not be called during the execution of f,
unless it calls [finalise_release]).
It can call [finalise] on [v] or other values to register other
functions or even itself. It can raise an exception; in this case
the exception will interrupt whatever the program was doing when
the function was called.
[finalise] will raise [Invalid_argument] if [v] is not
guaranteed to be heap-allocated. Some examples of values that are not
heap-allocated are integers, constant constructors, booleans,
the empty array, the empty list, the unit value. The exact list
of what is heap-allocated or not is implementation-dependent.
Some constant values can be heap-allocated but never deallocated
during the lifetime of the program, for example a list of integer
constants; this is also implementation-dependent.
Note that values of types [float] are sometimes allocated and
sometimes not, so finalising them is unsafe, and [finalise] will
also raise [Invalid_argument] for them. Values of type ['a Lazy.t]
(for any ['a]) are like [float] in this respect, except that the
compiler sometimes optimizes them in a way that prevents [finalise]
from detecting them. In this case, it will not raise
[Invalid_argument], but you should still avoid calling [finalise]
on lazy values.
The results of calling {!String.make}, {!Bytes.make}, {!Bytes.create},
{!Array.make}, and {!Stdlib.ref} are guaranteed to be
heap-allocated and non-constant except when the length argument is [0].
*)
val finalise_last : (unit -> unit) -> 'a -> unit
(** same as {!finalise} except the value is not given as argument. So
you can't use the given value for the computation of the
finalisation function. The benefit is that the function is called
after the value is unreachable for the last time instead of the
first time. So contrary to {!finalise} the value will never be
reachable again or used again. In particular every weak pointer
and ephemeron that contained this value as key or data is unset
before running the finalisation function. Moreover the finalisation
functions attached with {!finalise} are always called before the
finalisation functions attached with {!finalise_last}.
@since 4.04
*)
val finalise_release : unit -> unit
(** A finalisation function may call [finalise_release] to tell the
GC that it can launch the next finalisation function without waiting
for the current one to return. *)
type alarm
(** An alarm is a piece of data that calls a user function at the end of
each major GC cycle. The following functions are provided to create
and delete alarms. *)
val create_alarm : (unit -> unit) -> alarm
(** [create_alarm f] will arrange for [f] to be called at the end of each
major GC cycle, starting with the current cycle or the next one.
A value of type [alarm] is returned that you can
use to call [delete_alarm]. *)
val delete_alarm : alarm -> unit
(** [delete_alarm a] will stop the calls to the function associated
to [a]. Calling [delete_alarm a] again has no effect. *)
external eventlog_pause : unit -> unit = "caml_eventlog_pause"
(** [eventlog_pause ()] will pause the collection of traces in the
runtime.
Traces are collected if the program is linked to the instrumented runtime
and started with the environment variable OCAML_EVENTLOG_ENABLED.
Events are flushed to disk after pausing, and no new events will be
recorded until [eventlog_resume] is called. *)
external eventlog_resume : unit -> unit = "caml_eventlog_resume"
(** [eventlog_resume ()] will resume the collection of traces in the
runtime.
Traces are collected if the program is linked to the instrumented runtime
and started with the environment variable OCAML_EVENTLOG_ENABLED.
This call can be used after calling [eventlog_pause], or if the program
was started with OCAML_EVENTLOG_ENABLED=p. (which pauses the collection of
traces before the first event.) *)
(** [Memprof] is a sampling engine for allocated memory words. Every
allocated word has a probability of being sampled equal to a
configurable sampling rate. Once a block is sampled, it becomes
tracked. A tracked block triggers a user-defined callback as soon
as it is allocated, promoted or deallocated.
Since blocks are composed of several words, a block can potentially
be sampled several times. If a block is sampled several times, then
each of the callback is called once for each event of this block:
the multiplicity is given in the [n_samples] field of the
[allocation] structure.
This engine makes it possible to implement a low-overhead memory
profiler as an OCaml library.
Note: this API is EXPERIMENTAL. It may change without prior
notice. *)
module Memprof :
sig
type allocation = private
{ n_samples : int;
(** The number of samples in this block (>= 1). *)
size : int;
(** The size of the block, in words, excluding the header. *)
unmarshalled : bool;
(** Whether the block comes from unmarshalling. *)
callstack : Printexc.raw_backtrace
(** The callstack for the allocation. *)
}
(** The type of metadata associated with allocations. This is the
type of records passed to the callback triggered by the
sampling of an allocation. *)
type ('minor, 'major) tracker = {
alloc_minor: allocation -> 'minor option;
alloc_major: allocation -> 'major option;
promote: 'minor -> 'major option;
dealloc_minor: 'minor -> unit;
dealloc_major: 'major -> unit;
}
(**
A [('minor, 'major) tracker] describes how memprof should track
sampled blocks over their lifetime, keeping a user-defined piece
of metadata for each of them: ['minor] is the type of metadata
to keep for minor blocks, and ['major] the type of metadata
for major blocks.
If an allocation-tracking or promotion-tracking function returns [None],
memprof stops tracking the corresponding value.
*)
val null_tracker: ('minor, 'major) tracker
(** Default callbacks simply return [None] or [()] *)
val start :
sampling_rate:float ->
?callstack_size:int ->
('minor, 'major) tracker ->
unit
(** Start the sampling with the given parameters. Fails if
sampling is already active.
The parameter [sampling_rate] is the sampling rate in samples
per word (including headers). Usually, with cheap callbacks, a
rate of 1e-4 has no visible effect on performance, and 1e-3
causes the program to run a few percent slower
The parameter [callstack_size] is the length of the callstack
recorded at every sample. Its default is [max_int].
The parameter [tracker] determines how to track sampled blocks
over their lifetime in the minor and major heap.
Sampling is temporarily disabled when calling a callback
for the current thread. So they do not need to be reentrant if
the program is single-threaded. However, if threads are used,
it is possible that a context switch occurs during a callback,
in this case the callback functions must be reentrant.
Note that the callback can be postponed slightly after the
actual event. The callstack passed to the callback is always
accurate, but the program state may have evolved.
Calling [Thread.exit] in a callback is currently unsafe and can
result in undefined behavior. *)
val stop : unit -> unit
(** Stop the sampling. Fails if sampling is not active.
This function does not allocate memory, but tries to run the
postponed callbacks for already allocated memory blocks (of
course, these callbacks may allocate).
All the already tracked blocks are discarded.
Calling [stop] when a callback is running can lead to
callbacks not being called even though some events happened. *)
end
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