[PATCH v4 0/1] Add tracepoints around mmap_lock acquisition

From: Axel Rasmussen <axelrasmussen@google.com>
To: Steven Rostedt <rostedt@goodmis.org>,
	Ingo Molnar <mingo@redhat.com>,
	 Andrew Morton <akpm@linux-foundation.org>,
	Michel Lespinasse <walken@google.com>,
	 Vlastimil Babka <vbabka@suse.cz>,
	Daniel Jordan <daniel.m.jordan@oracle.com>,
	 Jann Horn <jannh@google.com>,
	Chinwen Chang <chinwen.chang@mediatek.com>,
	 Davidlohr Bueso <dbueso@suse.de>,
	David Rientjes <rientjes@google.com>
Cc: Yafang Shao <laoar.shao@gmail.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	 Axel Rasmussen <axelrasmussen@google.com>
Subject: [PATCH v4 0/1] Add tracepoints around mmap_lock acquisition
Date: Tue, 20 Oct 2020 11:47:45 -0700	[thread overview]
Message-ID: <20201020184746.300555-1-axelrasmussen@google.com> (raw)

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