This patchset adds tracepoints around mmap_lock acquisition. This is useful so we can measure the latency of lock acquisition, in order to detect contention. This version is based on v5.10-rc2. Changes since v5: - Michel pointed out that rwsem_release in mmap_read_trylock_non_owner doesn't actually release the lock, it just releases lockdep's ownership tracking. So, it's incorrect to call __mmap_lock_trace_released there, so the call has been removed. Changes since v4: - Redesigned buffer allocation to deal with the fact that a trace event might be interrupted by e.g. an IRQ, for which a per-cpu buffer is insufficient. Now we allocate one buffer per CPU * one buffer per context we might be called in (currently 4: normal, irq, softirq, NMI). We have three trace events which can potentially all be enabled, and all of which need a buffer; to avoid further multiplying the number of buffers by 3, they share the same set of buffers, which requires a spinlock + counter setup so we only allocate the buffers once, and then free them only when *all* of the trace events are _unreg()-ed. Changes since v3: - Switched EXPORT_SYMBOL to EXPORT_TRACEPOINT_SYMBOL, removed comment. - Removed redundant trace_..._enabled() check. - Defined the three TRACE_EVENTs separately, instead of sharing an event class. The tradeoff is 524 more bytes in .text, but the start_locking and released events no longer have a vestigial "success" field, so they're simpler + faster. Changes since v2: - Refactored tracing helper functions so the helpers are simper, but the locking functinos are slightly more verbose. Overall, this decreased the delta to mmap_lock.h slightly. - Fixed a typo in a comment. :) Changes since v1: - Functions renamed to reserve the "trace_" prefix for actual tracepoints. - We no longer measure the duration directly. Instead, users are expected to construct a synthetic event which computes the interval between "start locking" and "acquire returned". - The new helper for checking if tracepoints are enabled in a header is used to avoid un-inlining any of the lock wrappers. This yields ~zero overhead if the tracepoints aren't enabled, and therefore obviates the need for a Kconfig for this change. [1] https://lore.kernel.org/patchwork/patch/1316922/ [2] https://lore.kernel.org/patchwork/patch/1311996/ Axel Rasmussen (1): mmap_lock: add tracepoints around lock acquisition include/linux/mmap_lock.h | 94 +++++++++++++++- include/trace/events/mmap_lock.h | 107 ++++++++++++++++++ mm/Makefile | 2 +- mm/mmap_lock.c | 187 +++++++++++++++++++++++++++++++ 4 files changed, 384 insertions(+), 6 deletions(-) create mode 100644 include/trace/events/mmap_lock.h create mode 100644 mm/mmap_lock.c -- 2.29.1.341.ge80a0c044ae-goog
