linux-kernel - [PATCH v4 0/1] Add tracepoints around mmap

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Message-Id: <20201020184746.300555-1-axelrasmussen@google.com>
Date:   Tue, 20 Oct 2020 11:47:45 -0700
From:   Axel Rasmussen <axelrasmussen@...gle.com>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michel Lespinasse <walken@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        Jann Horn <jannh@...gle.com>,
        Chinwen Chang <chinwen.chang@...iatek.com>,
        Davidlohr Bueso <dbueso@...e.de>,
        David Rientjes <rientjes@...gle.com>
Cc:     Yafang Shao <laoar.shao@...il.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Axel Rasmussen <axelrasmussen@...gle.com>
Subject: [PATCH v4 0/1] Add tracepoints around mmap_lock acquisition

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 upon linux-next (since it depends on some recently-merged
patches [1] [2]).

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        | 93 ++++++++++++++++++++++++++++--
 include/trace/events/mmap_lock.h | 98 ++++++++++++++++++++++++++++++++
 mm/Makefile                      |  2 +-
 mm/mmap_lock.c                   | 80 ++++++++++++++++++++++++++
 4 files changed, 267 insertions(+), 6 deletions(-)
 create mode 100644 include/trace/events/mmap_lock.h
 create mode 100644 mm/mmap_lock.c

--
2.29.0.rc1.297.gfa9743e501-goog