Home
Reading
Searching
Subscribe
Sponsors
Statistics
Posting
Contact
Spam
Lists
Links
About
Hosting
Filtering
Features Download
Marketing
Archives
FAQ
Blog
 
Gmane
From: Mel Gorman <mel <at> csn.ul.ie>
Subject: [PATCH 0/4] Add some trace events for the page allocator v4
Newsgroups: gmane.linux.kernel
Date: Thursday 6th August 2009 16:07:01 UTC (over 7 years ago)
This is V4 of a patchset to add some trace points for the page allocator.
The
largest changes in this version is performance improvements and expansion
of the post-processing script as well as some documentation. There were
minor changes
elsewhere that are described in the changelog.

Changelog since V3
  o Drop call_site information from trace events
  o Use struct page * instead of void * in trace events
  o Add CPU information to the per-cpu tracepoints information
  o Improved performance of offline-process script so it can run online
  o Add support for interrupting processing script to dump what it has
  o Add support for stripping pids, getting additional information from
    proc and adding information on the parent process
  o Improve layout of output of post processing script for use with sort
  o Add documentation on performance analysis using tracepoints
  o Add documentation on the kmem tracepoints in particular

Changelog since V2
  o Added Ack-ed By's from Rik
  o Only call trace_mm_page_free_direct when page count reaches zero
  o Rebase to 2.6.31-rc5

Changelog since V1
  o Fix minor formatting error for the __rmqueue event
  o Add event for __pagevec_free
  o Bring naming more in line with Larry Woodman's tracing patch
  o Add an example post-processing script for the trace events

The following four patches add some trace events for the page allocator
under the heading of kmem.

	Patch 1 adds events for plain old allocate and freeing of pages
	Patch 2 gives information useful for analysing fragmentation avoidance
	Patch 3 tracks pages going to and from the buddy lists as an indirect
		indication of zone lock hotness
	Patch 4 adds a post-processing script that aggegates the events to
		give a higher-level view
	Patch 5 adds documentation on analysis using tracepoints
	Patch 6 adds documentation on the kmem tracepoints in particular

The first set of events can be used as an indicator as to whether the
workload
was heavily dependant on the page allocator or not. You can make a guess
based
on vmstat but you can't get a per-process breakdown. Depending on the call
path, the call_site for page allocation may be __get_free_pages() instead
of a useful callsite. Instead of passing down a return address similar to
slab debugging, the user should enable the stacktrace and seg-addr options
to get a proper stack trace.

The second patch is mainly of use to users of hugepages and particularly
dynamic hugepage pool resizing as it could be used to tune min_free_kbytes
to a level that fragmentation was rarely a problem. My main concern is
that maybe I'm trying to jam too much into the TP_printk that could be
extrapolated after the fact if you were familiar with the implementation. I
couldn't determine if it was best to hold the hand of the administrator
even if it cost more to figure it out.

The third patch is trickier to draw conclusions from but high activity on
those events could explain why there were a large number of cache misses
on a page-allocator-intensive workload. The coalescing and splitting of
buddies involves a lot of writing of page metadata and cache line bounces
not to mention the acquisition of an interrupt-safe lock necessary to enter
this path.

The fourth patch parses the trace buffer to draw a higher-level picture of
what is going on broken down on a per-process basis.

The last two patches add documentation.

 Documentation/trace/events-kmem.txt                |  107 ++++++
 .../postprocess/trace-pagealloc-postprocess.pl     |  356
++++++++++++++++++++
 Documentation/trace/tracepoint-analysis.txt        |  327
++++++++++++++++++
 include/trace/events/kmem.h                        |  177 ++++++++++
 mm/page_alloc.c                                    |   16 +-
 5 files changed, 982 insertions(+), 1 deletions(-)
 create mode 100644 Documentation/trace/events-kmem.txt
 create mode 100755
Documentation/trace/postprocess/trace-pagealloc-postprocess.pl
 create mode 100644 Documentation/trace/tracepoint-analysis.txt

Mel Gorman (6):
  tracing, page-allocator: Add trace events for page allocation and
    page freeing
  tracing, page-allocator: Add trace events for anti-fragmentation
    falling back to other migratetypes
  tracing, page-allocator: Add trace event for page traffic related to
    the buddy lists
  tracing, page-allocator: Add a postprocessing script for
    page-allocator-related ftrace events
  tracing, documentation: Add a document describing how to do some
    performance analysis with tracepoints
  tracing, documentation: Add a document on the kmem tracepoints

 Documentation/trace/events-kmem.txt                |  107 ++++++
 .../postprocess/trace-pagealloc-postprocess.pl     |  356
++++++++++++++++++++
 Documentation/trace/tracepoint-analysis.txt        |  327
++++++++++++++++++
 include/trace/events/kmem.h                        |  177 ++++++++++
 mm/page_alloc.c                                    |   15 +-
 5 files changed, 981 insertions(+), 1 deletions(-)
 create mode 100644 Documentation/trace/events-kmem.txt
 create mode 100755
Documentation/trace/postprocess/trace-pagealloc-postprocess.pl
 create mode 100644 Documentation/trace/tracepoint-analysis.txt

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to [email protected]  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email:  email@kvack.org 
 
CD: 4ms