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    Subject[PATCH 0/2] tracing/mm: Add tracepoint_enabled() helper function for headers
    Tracepoints are not safe to be called directly from header files as they may
    be included by C code that has CREATE_TRACE_POINTS defined, and this would
    cause side effects and possibly break the build in hard to debug ways.

    Instead, it is recommended to call a tracepoint helper function that is
    defined in a C file that calls the tracepoint. But we would only want this
    function to be called if the tracepoint is enabled, as function calls add
    overhead.

    The trace_<tracepoint>_enabled() function is also no safe to be called in a
    header file as it is created by the tracepoint header, which suffers the
    same fate if CREATE_TRACE_POINTS is defined. Instead, the tracepoint needs
    to be declared as an extern, and the helper function can test the static key
    to call the helper function that calls the tracepoint.

    This has been done by open coding the tracepoint extern and calling the
    static key directly:

    commit 95813b8faa0cd ("mm/page_ref: add tracepoint to track down page
    reference manipulation")

    does this (back in 2016). Now we have another use case, so a helper function
    should be created to keep the internals of the tracepoints from being spread
    out in other subsystems.

    Link: https://lore.kernel.org/r/20200922125113.12ef1e03@gandalf.local.home

    This adds tracepoint_enabled() helper macro and DECLARE_TRACEPOINT() macro
    to allow this to be done without exposing the internals of the tracepoints.

    The first patch adds the infrastructure, the second converts page_ref over
    to it. I also noticed that the msr tracepoint needs to be converted as well.


    Steven Rostedt (VMware) (2):
    tracepoints: Add helper to test if tracepoint is enabled in a header
    mm/page_ref: Convert the open coded tracepoint enabled to the new helper

    ----
    Documentation/trace/tracepoints.rst | 25 ++++++++++++++++++++++
    include/linux/page_ref.h | 42 ++++++++++++++++++-------------------
    include/linux/tracepoint-defs.h | 33 +++++++++++++++++++++++++++++
    3 files changed, 79 insertions(+), 21 deletions(-)

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