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From: SeongJae Park <sjpark@amazon.com>
To: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
Cc: SeongJae Park <sjpark@amazon.com>, <akpm@linux-foundation.org>,
	"SeongJae Park" <sjpark@amazon.de>, <aarcange@redhat.com>,
	<yang.shi@linux.alibaba.com>, <acme@kernel.org>,
	<alexander.shishkin@linux.intel.com>, <amit@kernel.org>,
	<brendan.d.gregg@gmail.com>, <brendanhiggins@google.com>,
	<cai@lca.pw>, <colin.king@canonical.com>, <corbet@lwn.net>,
	<dwmw@amazon.com>, <jolsa@redhat.com>, <kirill@shutemov.name>,
	<mark.rutland@arm.com>, <mgorman@suse.de>, <minchan@kernel.org>,
	<mingo@redhat.com>, <namhyung@kernel.org>, <peterz@infradead.org>,
	<rdunlap@infradead.org>, <rientjes@google.com>,
	<rostedt@goodmis.org>, <shuah@kernel.org>, <sj38.park@gmail.com>,
	<vbabka@suse.cz>, <vdavydov.dev@gmail.com>, <linux-mm@kvack.org>,
	<linux-doc@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: Re: [PATCH v6 11/14] Documentation/admin-guide/mm: Add a document for DAMON
Date: Tue, 10 Mar 2020 12:57:55 +0100
Message-ID: <20200310115755.25270-1-sjpark@amazon.com> (raw)
In-Reply-To: <20200310090348.000077d5@Huawei.com> (raw)

On Tue, 10 Mar 2020 09:03:48 +0000 Jonathan Cameron <Jonathan.Cameron@Huawei.com> wrote:

> On Mon, 24 Feb 2020 13:30:44 +0100
> SeongJae Park <sjpark@amazon.com> wrote:
> 
> > From: SeongJae Park <sjpark@amazon.de>
> > 
> > This commit adds a simple document for DAMON under
> > `Documentation/admin-guide/mm`.
> > 
> 
> Nice document to get people started.
> 
> Certainly worked for me doing some initial playing around.

Great to hear that :)

> 
> In general this is an interesting piece of work.   I can see there are numerous
> possible avenues to explore in making the monitoring more flexible, or potentially
> better at tracking usage whilst not breaking your fundamental 'bounded overhead'
> requirement.   Will be fun perhaps to explore some of those.
> 
> I'll do some more exploring and perhaps try some real world workloads.
> 
> Thanks,
> 
> Jonathan
> 
> 
> > Signed-off-by: SeongJae Park <sjpark@amazon.de>
> > ---
> >  .../admin-guide/mm/data_access_monitor.rst    | 414 ++++++++++++++++++
> >  Documentation/admin-guide/mm/index.rst        |   1 +
> >  2 files changed, 415 insertions(+)
> >  create mode 100644 Documentation/admin-guide/mm/data_access_monitor.rst
> > 
> > diff --git a/Documentation/admin-guide/mm/data_access_monitor.rst b/Documentation/admin-guide/mm/data_access_monitor.rst
> > new file mode 100644
> > index 000000000000..4d836c3866e2
> > --- /dev/null
> > +++ b/Documentation/admin-guide/mm/data_access_monitor.rst
> > @@ -0,0 +1,414 @@
> > +.. SPDX-License-Identifier: GPL-2.0
> > +
> > +==========================
> > +DAMON: Data Access MONitor
> > +==========================
> > +
> > +Introduction
> > +============
> > +
> > +Memory management decisions can normally be more efficient if finer data access
> > +information is available.  However, because finer information usually comes
> > +with higher overhead, most systems including Linux made a tradeoff: Forgive
> > +some wise decisions and use coarse information and/or light-weight heuristics.
> 
> I'm not sure what "Forgive some wise decisions" means...

I wanted to mean that the mechanism makes no optimal decisions.  Will wordsmith
again.

> 
> > +
> > +A number of experimental data access pattern awared memory management
> > +optimizations say the sacrifices are
> > +huge (2.55x slowdown).  
> 
> Good to have a reference.

:)

> 
> > However, none of those has successfully adopted to
> 
> adopted into the 

Thanks for correcting.

> 
[...]
> > +Applying Dynamic Memory Mappings
> > +--------------------------------
> > +
> > +Only a number of small parts in the super-huge virtual address space of the
> > +processes is mapped to physical memory and accessed.  Thus, tracking the
> > +unmapped address regions is just wasteful.  However, tracking every memory
> > +mapping change might incur an overhead.  For the reason, DAMON applies the
> > +dynamic memory mapping changes to the tracking regions only for each of an
> > +user-specified time interval (``regions update interval``).
> 
> One key part of the approach is the 3 region bit.  Perhaps talk about that here
> somewhere?

I was afraid if it is too implementation detail, as this document is for admin
users.  Will add it in next spin, though.

> 
> > +
> > +
> > +``debugfs`` Interface
> > +=====================
> > +
> > +DAMON exports four files, ``attrs``, ``pids``, ``record``, and ``monitor_on``
> > +under its debugfs directory, ``<debugfs>/damon/``.
> > +
> > +Attributes
> > +----------
> > +
> > +Users can read and write the ``sampling interval``, ``aggregation interval``,
> > +``regions update interval``, and min/max number of monitoring target regions by
> > +reading from and writing to the ``attrs`` file.  For example, below commands
> > +set those values to 5 ms, 100 ms, 1,000 ms, 10, 1000 and check it again::
> > +
> > +    # cd <debugfs>/damon
> > +    # echo 5000 100000 1000000 10 1000 > attrs
> 
> I'm personally a great fan of human readable interfaces.  Could we just
> split this into one file per interval?  That way the file naming would
> make it self describing.

I was worried if it makes too many files.  Do you think it's ok?

> 
> > +    # cat attrs
> > +    5000 100000 1000000 10 1000
> > +
> > +Target PIDs
> > +-----------
> > +
> > +Users can read and write the pids of current monitoring target processes by
> > +reading from and writing to the ``pids`` file.  For example, below commands set
> > +processes having pids 42 and 4242 as the processes to be monitored and check it
> > +again::
> > +
> > +    # cd <debugfs>/damon
> > +    # echo 42 4242 > pids
> > +    # cat pids
> > +    42 4242
> > +
> > +Note that setting the pids doesn't starts the monitoring.
> > +
> > +Record
> > +------
> > +
> > +DAMON support direct monitoring result record feature.  The recorded results
> > +are first written to a buffer and flushed to a file in batch.  Users can set
> > +the size of the buffer and the path to the result file by reading from and
> > +writing to the ``record`` file.  For example, below commands set the buffer to
> > +be 4 KiB and the result to be saved in ``/damon.data``.
> > +
> > +    # cd <debugfs>/damon
> > +    # echo "4096 /damon.data" > pids
> 
> write it to record, not pids.

Ah, good eye!

> 
> > +    # cat record
> > +    4096 /damon.data
> > +
> > +Turning On/Off
> > +--------------
> > +
> > +You can check current status, start and stop the monitoring by reading from and
> > +writing to the ``monitor_on`` file.  Writing ``on`` to the file starts DAMON to
> > +monitor the target processes with the attributes.  Writing ``off`` to the file
> > +stops DAMON.  DAMON also stops if every target processes is be terminated.
> > +Below example commands turn on, off, and check status of DAMON::
> > +
> > +    # cd <debugfs>/damon
> > +    # echo on > monitor_on
> > +    # echo off > monitor_on
> > +    # cat monitor_on
> > +    off
> > +
> > +Please note that you cannot write to the ``attrs`` and ``pids`` files while the
> > +monitoring is turned on.  If you write to the files while DAMON is running,
> > +``-EINVAL`` will be returned.
> 
> Perhaps -EBUSY would be more informative?  Implies values might be fine, but
> the issue is 'not now'.

Agreed, will change so!


Thanks,
SeongJae Park

[...]


  reply index

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-24 12:30 [PATCH v6 00/14] Introduce Data Access MONitor (DAMON) SeongJae Park
2020-02-24 12:30 ` [PATCH v6 01/14] mm: " SeongJae Park
2020-03-10  8:54   ` Jonathan Cameron
2020-03-10 11:50     ` SeongJae Park
2020-02-24 12:30 ` [PATCH v6 02/14] mm/damon: Implement region based sampling SeongJae Park
2020-03-10  8:57   ` Jonathan Cameron
2020-03-10 11:52     ` SeongJae Park
2020-03-10 15:55       ` Jonathan Cameron
2020-03-10 16:22         ` SeongJae Park
2020-03-10 17:39           ` Jonathan Cameron
2020-03-12  9:20             ` SeongJae Park
2020-03-13 17:29   ` Jonathan Cameron
2020-03-13 20:16     ` SeongJae Park
2020-03-17 11:32       ` SeongJae Park
2020-02-24 12:30 ` [PATCH v6 03/14] mm/damon: Adaptively adjust regions SeongJae Park
2020-03-10  8:57   ` Jonathan Cameron
2020-03-10 11:53     ` SeongJae Park
2020-02-24 12:30 ` [PATCH v6 04/14] mm/damon: Apply dynamic memory mapping changes SeongJae Park
2020-03-10  9:00   ` Jonathan Cameron
2020-03-10 11:53     ` SeongJae Park
2020-02-24 12:30 ` [PATCH v6 05/14] mm/damon: Implement callbacks SeongJae Park
2020-03-10  9:01   ` Jonathan Cameron
2020-03-10 11:55     ` SeongJae Park
2020-02-24 12:30 ` [PATCH v6 06/14] mm/damon: Implement access pattern recording SeongJae Park
2020-03-10  9:01   ` Jonathan Cameron
2020-03-10 11:55     ` SeongJae Park
2020-02-24 12:30 ` [PATCH v6 07/14] mm/damon: Implement kernel space API SeongJae Park
2020-03-10  9:01   ` Jonathan Cameron
2020-03-10 11:56     ` SeongJae Park
2020-02-24 12:30 ` [PATCH v6 08/14] mm/damon: Add debugfs interface SeongJae Park
2020-03-10  9:02   ` Jonathan Cameron
2020-03-10 11:56     ` SeongJae Park
2020-02-24 12:30 ` [PATCH v6 09/14] mm/damon: Add a tracepoint for result writing SeongJae Park
2020-03-10  9:03   ` Jonathan Cameron
2020-03-10 11:57     ` SeongJae Park
2020-02-24 12:30 ` [PATCH v6 10/14] tools: Add a minimal user-space tool for DAMON SeongJae Park
2020-02-24 12:30 ` [PATCH v6 11/14] Documentation/admin-guide/mm: Add a document " SeongJae Park
2020-03-10  9:03   ` Jonathan Cameron
2020-03-10 11:57     ` SeongJae Park [this message]
2020-02-24 12:30 ` [PATCH v6 12/14] mm/damon: Add kunit tests SeongJae Park
2020-02-24 12:30 ` [PATCH v6 13/14] mm/damon: Add user selftests SeongJae Park
2020-02-24 12:30 ` [PATCH v6 14/14] MAINTAINERS: Update for DAMON SeongJae Park
2020-03-02 11:35 ` [PATCH v6 00/14] Introduce Data Access MONitor (DAMON) SeongJae Park
2020-03-09 10:23   ` SeongJae Park
2020-03-10 17:21 ` Shakeel Butt
2020-03-12 10:07   ` SeongJae Park
2020-03-12 10:43     ` SeongJae Park
2020-03-18 19:52       ` Shakeel Butt
2020-03-19  9:03         ` SeongJae Park
2020-03-23 17:29           ` Shakeel Butt
2020-03-24  8:34             ` SeongJae Park

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