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@node Internal Probes
@c @node Internal Probes, , POSIX Threads, Top
@c %MENU% Probes to monitor libc internal behavior
@chapter Internal probes
In order to aid in debugging and monitoring internal behavior,
@theglibc{} exposes nearly-zero-overhead SystemTap probes marked with
the @code{libc} provider.
These probes are not part of the @glibcadj{} stable ABI, and they are
subject to change or removal across releases. Our only promise with
regard to them is that, if we find a need to remove or modify the
arguments of a probe, the modified probe will have a different name, so
that program monitors relying on the old probe will not get unexpected
arguments.
@menu
* Memory Allocation Probes:: Probes in the memory allocation subsystem
@end menu
@node Memory Allocation Probes
@section Memory Allocation Probes
These probes are designed to signal relatively unusual situations within
the virtual memory subsystem of @theglibc{}. The location and the
availability of some probes depend on whether per-thread arenas are
enabled (the default) or disabled at the time @theglibc{} is compiled.
@deftp Probe memory_arena_new (void *@var{$arg1}, size_t @var{$arg2})
This probe is triggered when @code{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 @code{malloc_state} internal data structure is
located at @var{$arg1}, within a newly-allocated heap big enough to hold
at least @var{$arg2} bytes.
@end deftp
@deftp Probe memory_mallopt (int @var{$arg1}, int @var{$arg2})
This probe is triggered when function @code{mallopt} is called to change
@code{malloc} internal configuration parameters, before any change to
the parameters is made. The arguments @var{$arg1} and @var{$arg2} are
the ones passed to the @code{mallopt} function.
@end deftp
@deftp Probe memory_mallopt_mxfast (int @var{$arg1}, int @var{$arg2})
This probe is triggered shortly after the @code{memory_mallopt} probe,
when the parameter to be changed is @code{M_MXFAST}, and the requested
value is in an acceptable range. Argument @var{$arg1} is the requested
value, and @var{$arg2} is the previous value of this @code{malloc}
parameter.
@end deftp
@deftp Probe memory_mallopt_trim_threshold (int @var{$arg1}, int @var{$arg2}, int @var{$arg3})
This probe is triggere shortly after the @code{memory_mallopt} probe,
when the parameter to be changed is @code{M_TRIM_THRESHOLD}. Argument
@var{$arg1} is the requested value, @var{$arg2} is the previous value of
this @code{malloc} parameter, and @var{$arg3} is nonzero if dynamic
threshold adjustment was already disabled.
@end deftp
@deftp Probe memory_mallopt_top_pad (int @var{$arg1}, int @var{$arg2}, int @var{$arg3})
This probe is triggered shortly after the @code{memory_mallopt} probe,
when the parameter to be changed is @code{M_TOP_PAD}. Argument
@var{$arg1} is the requested value, @var{$arg2} is the previous value of
this @code{malloc} parameter, and @var{$arg3} is nonzero if dynamic
threshold adjustment was already disabled.
@end deftp
@deftp Probe memory_mallopt_mmap_threshold (int @var{$arg1}, int @var{$arg2}, int @var{$arg3})
This probe is triggered shortly after the @code{memory_mallopt} probe,
when the parameter to be changed is @code{M_MMAP_THRESHOLD}, and the
requested value is in an acceptable range. Argument @var{$arg1} is the
requested value, @var{$arg2} is the previous value of this @code{malloc}
parameter, and @var{$arg3} is nonzero if dynamic threshold adjustment
was already disabled.
@end deftp
@deftp Probe memory_mallopt_mmap_max (int @var{$arg1}, int @var{$arg2}, int @var{$arg3})
This probe is triggered shortly after the @code{memory_mallopt} probe,
when the parameter to be changed is @code{M_MMAP_MAX}. Argument
@var{$arg1} is the requested value, @var{$arg2} is the previous value of
this @code{malloc} parameter, and @var{$arg3} is nonzero if dynamic
threshold adjustment was already disabled.
@end deftp
@deftp Probe memory_mallopt_check_action (int @var{$arg1}, int @var{$arg2})
This probe is triggered shortly after the @code{memory_mallopt} probe,
when the parameter to be changed is @code{M_CHECK_ACTION}. Argument
@var{$arg1} is the requested value, and @var{$arg2} is the previous
value of this @code{malloc} parameter.
@end deftp
@deftp Probe memory_mallopt_perturb (int @var{$arg1}, int @var{$arg2})
This probe is triggered shortly after the @code{memory_mallopt} probe,
when the parameter to be changed is @code{M_PERTURB}. Argument
@var{$arg1} is the requested value, and @var{$arg2} is the previous
value of this @code{malloc} parameter.
@end deftp
@deftp Probe memory_mallopt_arena_test (int @var{$arg1}, int @var{$arg2})
This probe is triggered shortly after the @code{memory_mallopt} probe,
when the parameter to be changed is @code{M_ARENA_TEST}, and the
requested value is in an acceptable range. Argument @var{$arg1} is the
requested value, and @var{$arg2} is the previous value of this
@code{malloc} parameter. This probe is only available when per-thread
arenas are enabled.
@end deftp
@deftp Probe memory_mallopt_arena_max (int @var{$arg1}, int @var{$arg2})
This probe is triggered shortly after the @code{memory_mallopt} probe,
when the parameter to be changed is @code{M_ARENA_MAX}, and the
requested value is in an acceptable range. Argument @var{$arg1} is the
requested value, and @var{$arg2} is the previous value of this
@code{malloc} parameter. This probe is only available when per-thread
arenas are enabled.
@end deftp
@deftp Probe memory_mallopt_free_dyn_thresholds (int @var{$arg1}, int @var{$arg2})
This probe is triggered when function @code{free} decides to adjust the
dynamic brk/mmap thresholds. Argument @var{$arg1} and @var{$arg2} are
the adjusted mmap and trim thresholds, respectively.
@end deftp
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