(libc.info.gz) Memory Allocation Probes
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(libc.info.gz) Internal Probes
36.1 Memory Allocation Probes
=============================
These probes are designed to signal relatively unusual situations within
the virtual memory subsystem of the GNU C Library. The location and the
availability of some probes depend on whether per-thread arenas are
enabled (the default) or disabled at the time the GNU C Library is
compiled.
-- Probe: memory_sbrk_more (void *$ARG1, size_t $ARG2)
This probe is triggered after the main arena is extended by calling
'sbrk'. Argument $ARG1 is the additional size requested to 'sbrk',
and $ARG2 is the pointer that marks the end of the 'sbrk' area,
returned in response to the request.
-- Probe: memory_sbrk_less (void *$ARG1, size_t $ARG2)
This probe is triggered after the size of the main arena is
decreased by calling 'sbrk'. Argument $ARG1 is the size released
by 'sbrk' (the positive value, rather than the negative value
passed to 'sbrk'), and $ARG2 is the pointer that marks the end of
the 'sbrk' area, returned in response to the request.
-- Probe: memory_heap_new (void *$ARG1, size_t $ARG2)
This probe is triggered after a new heap is 'mmap'ed. Argument
$ARG1 is a pointer to the base of the memory area, where the
'heap_info' data structure is held, and $ARG2 is the size of the
heap.
-- Probe: memory_heap_free (void *$ARG1, size_t $ARG2)
This probe is triggered _before_ (unlike the other sbrk and heap
probes) a heap is completely removed via 'munmap'. Argument $ARG1
is a pointer to the heap, and $ARG2 is the size of the heap.
-- Probe: memory_heap_more (void *$ARG1, size_t $ARG2)
This probe is triggered after a trailing portion of an 'mmap'ed
heap is extended. Argument $ARG1 is a pointer to the heap, and
$ARG2 is the new size of the heap.
-- Probe: memory_heap_less (void *$ARG1, size_t $ARG2)
This probe is triggered after a trailing portion of an 'mmap'ed
heap is released. Argument $ARG1 is a pointer to the heap, and
$ARG2 is the new size of the heap.
-- Probe: memory_malloc_retry (size_t $ARG1)
-- Probe: memory_realloc_retry (size_t $ARG1, void *$ARG2)
-- Probe: memory_memalign_retry (size_t $ARG1, size_t $ARG2)
-- Probe: memory_valloc_retry (size_t $ARG1)
-- Probe: memory_pvalloc_retry (size_t $ARG1)
-- Probe: memory_calloc_retry (size_t $ARG1)
These probes are triggered when the corresponding functions fail to
obtain the requested amount of memory from the arena in use, before
they call 'arena_get_retry' to select an alternate arena in which
to retry the allocation. Argument $ARG1 is the amount of memory
requested by the user; in the 'calloc' case, that is the total size
computed from both function arguments. In the 'realloc' case,
$ARG2 is the pointer to the memory area being resized. In the
'memalign' case, $ARG2 is the alignment to be used for the request,
which may be stricter than the value passed to the 'memalign'
function.
Note that the argument order does _not_ match that of the
corresponding two-argument functions, so that in all of these
probes the user-requested allocation size is in $ARG1.
-- Probe: memory_arena_retry (size_t $ARG1, void *$ARG2)
This probe is triggered within 'arena_get_retry' (the function
called to select the alternate arena in which to retry an
allocation that failed on the first attempt), before the selection
of an alternate arena. This probe is redundant, but much easier to
use when it's not important to determine which of the various
memory allocation functions is failing to allocate on the first
try. Argument $ARG1 is the same as in the function-specific
probes, except for extra room for padding introduced by functions
that have to ensure stricter alignment. Argument $ARG2 is the
arena in which allocation failed.
-- Probe: memory_arena_new (void *$ARG1, size_t $ARG2)
This probe is triggered when 'malloc' allocates and initializes an
additional arena (not the main arena), but before the arena is
assigned to the running thread or inserted into the internal linked
list of arenas. The arena's 'malloc_state' internal data structure
is located at $ARG1, within a newly-allocated heap big enough to
hold at least $ARG2 bytes.
-- Probe: memory_arena_reuse (void *$ARG1, void *$ARG2)
This probe is triggered when 'malloc' has just selected an existing
arena to reuse, and (temporarily) reserved it for exclusive use.
Argument $ARG1 is a pointer to the newly-selected arena, and $ARG2
is a pointer to the arena previously used by that thread.
When per-thread arenas are enabled, this occurs within
'reused_arena', right after the mutex mentioned in probe
'memory_arena_reuse_wait' is acquired; argument $ARG1 will point to
the same arena. In this configuration, this will usually only
occur once per thread. The exception is when a thread first
selected the main arena, but a subsequent allocation from it fails:
then, and only then, may we switch to another arena to retry that
allocations, and for further allocations within that thread.
When per-thread arenas are disabled, this occurs within
'arena_get2', whenever the mutex for the previously-selected arena
cannot be immediately acquired.
-- Probe: memory_arena_reuse_wait (void *$ARG1, void *$ARG2, void
*$ARG3)
This probe is triggered when 'malloc' is about to wait for an arena
to become available for reuse. Argument $ARG1 holds a pointer to
the mutex the thread is going to wait on, $ARG2 is a pointer to a
newly-chosen arena to be reused, and $ARG3 is a pointer to the
arena previously used by that thread.
When per-thread arenas are enabled, this occurs within
'reused_arena', when a thread first tries to allocate memory or
needs a retry after a failure to allocate from the main arena,
there isn't any free arena, the maximum number of arenas has been
reached, and an existing arena was chosen for reuse, but its mutex
could not be immediately acquired. The mutex in $ARG1 is the mutex
of the selected arena.
When per-thread arenas are disabled, this occurs within
'arena_get2', when a thread first tries to allocate memory or the
mutex of the arena it previously used could not be immediately
acquired, and none of the existing arenas could be immediately
reserved for exclusive use. The mutex in $ARG1 is that of the list
of arenas, and since the arena won't have been selected yet, $ARG2
will be 'NULL'.
-- Probe: memory_arena_reuse_free_list (void *$ARG1)
This probe is triggered when 'malloc' has chosen an arena that is
in the free list for use by a thread, within the 'get_free_list'
function. This probe is only available when 'malloc' is configured
to use per-thread arenas. The argument $ARG1 holds a pointer to
the selected arena.
-- Probe: memory_arena_reuse_realloc (void *$ARG1)
This probe is triggered within 'realloc', as the arena of the
current thread is changed to match that in which the given address
was allocated. This probe is _not_ available when 'malloc' is
configured to use per-thread arenas. The argument $ARG1 holds a
pointer to the newly-selected arena.
-- Probe: memory_mallopt (int $ARG1, int $ARG2)
This probe is triggered when function 'mallopt' is called to change
'malloc' internal configuration parameters, before any change to
the parameters is made. The arguments $ARG1 and $ARG2 are the ones
passed to the 'mallopt' function.
-- Probe: memory_mallopt_mxfast (int $ARG1, int $ARG2)
This probe is triggered shortly after the 'memory_mallopt' probe,
when the parameter to be changed is 'M_MXFAST', and the requested
value is in an acceptable range. Argument $ARG1 is the requested
value, and $ARG2 is the previous value of this 'malloc' parameter.
-- Probe: memory_mallopt_trim_threshold (int $ARG1, int $ARG2, int
$ARG3)
This probe is triggere shortly after the 'memory_mallopt' probe,
when the parameter to be changed is 'M_TRIM_THRESHOLD'. Argument
$ARG1 is the requested value, $ARG2 is the previous value of this
'malloc' parameter, and $ARG3 is nonzero if dynamic threshold
adjustment was already disabled.
-- Probe: memory_mallopt_top_pad (int $ARG1, int $ARG2, int $ARG3)
This probe is triggered shortly after the 'memory_mallopt' probe,
when the parameter to be changed is 'M_TOP_PAD'. Argument $ARG1 is
the requested value, $ARG2 is the previous value of this 'malloc'
parameter, and $ARG3 is nonzero if dynamic threshold adjustment was
already disabled.
-- Probe: memory_mallopt_mmap_threshold (int $ARG1, int $ARG2, int
$ARG3)
This probe is triggered shortly after the 'memory_mallopt' probe,
when the parameter to be changed is 'M_MMAP_THRESHOLD', and the
requested value is in an acceptable range. Argument $ARG1 is the
requested value, $ARG2 is the previous value of this 'malloc'
parameter, and $ARG3 is nonzero if dynamic threshold adjustment was
already disabled.
-- Probe: memory_mallopt_mmap_max (int $ARG1, int $ARG2, int $ARG3)
This probe is triggered shortly after the 'memory_mallopt' probe,
when the parameter to be changed is 'M_MMAP_MAX'. Argument $ARG1
is the requested value, $ARG2 is the previous value of this
'malloc' parameter, and $ARG3 is nonzero if dynamic threshold
adjustment was already disabled.
-- Probe: memory_mallopt_check_action (int $ARG1, int $ARG2)
This probe is triggered shortly after the 'memory_mallopt' probe,
when the parameter to be changed is 'M_CHECK_ACTION'. Argument
$ARG1 is the requested value, and $ARG2 is the previous value of
this 'malloc' parameter.
-- Probe: memory_mallopt_perturb (int $ARG1, int $ARG2)
This probe is triggered shortly after the 'memory_mallopt' probe,
when the parameter to be changed is 'M_PERTURB'. Argument $ARG1 is
the requested value, and $ARG2 is the previous value of this
'malloc' parameter.
-- Probe: memory_mallopt_arena_test (int $ARG1, int $ARG2)
This probe is triggered shortly after the 'memory_mallopt' probe,
when the parameter to be changed is 'M_ARENA_TEST', and the
requested value is in an acceptable range. Argument $ARG1 is the
requested value, and $ARG2 is the previous value of this 'malloc'
parameter. This probe is only available when per-thread arenas are
enabled.
-- Probe: memory_mallopt_arena_max (int $ARG1, int $ARG2)
This probe is triggered shortly after the 'memory_mallopt' probe,
when the parameter to be changed is 'M_ARENA_MAX', and the
requested value is in an acceptable range. Argument $ARG1 is the
requested value, and $ARG2 is the previous value of this 'malloc'
parameter. This probe is only available when per-thread arenas are
enabled.
-- Probe: memory_mallopt_free_dyn_thresholds (int $ARG1, int $ARG2)
This probe is triggered when function 'free' decides to adjust the
dynamic brk/mmap thresholds. Argument $ARG1 and $ARG2 are the
adjusted mmap and trim thresholds, respectively.
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(libc.info.gz) Internal Probes
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