[TECH TOPIC] Writing a fine-grained access pattern oriented lightweight kernel module using DAMON/DAMOS in 10 minutes

[SeongJae Park <sj38.park@gmail.com>]

From: SeongJae Park <sjpark@amazon.de>

I mistakenly sent the mail to ksummit-discuss@lists.linux.dev, not
ksummit@lists.linux.dev.  Sending again, sorry.

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DAMON and DAMOS
---------------

DAMON[1] is a framework for general data access monitoring of kernel
subsystems.  It provides best-effort high quality monitoring results while
incurring only minimal and upper-bounded overhead, due to its practical
overhead-accuracy tradeoff mechanism.  On a production machine utilizing 70 GB
memory, it can repeatedly scan accesses to the whole memory for every 5ms,
while consuming only 1% single CPU time.

On top of it, a data access pattern-oriented memory management engine called
DAMON-based Operation Schemes (DAMOS) is implemented.  It allows clients to
implement their access pattern oriented memory management logic with very
simple scheme descriptions.  We implemented fine-grained access-aware THP and
proactive reclamation using this engine in three lines of scheme and achieved
remarkable improvements[2].

As of this writing (2021-05-28), the code is not in the mainline but available
at its development tree[3], and regularly posted to LKML as patchsets[4,5,6].
Nevertheless, the code has already merged in the public Amazon Linux kernel
trees[7,8], and all Amazon Linux users can use DAMON/DAMOS off the box. We are
also supporting the two latest upstream LTS stable kernels[9,10].

Agenda
------

In this talk, I will briefly introduce DAMON/DAMOS and present how you can
write a fine-grained data access pattern oriented lightweight kernel module on
top of DAMON/DAMOS.  With the talk, I will write an example module and evaluate
its performance on live.  A data access-aware proactive reclamation kernel
module for production use will also introduced as a use case.  After that, I
will discuss my future plans for improving DAMON and improving other kernel
subsystems using DAMON/DAMOS.

[1] https://damonitor.github.io (https://damonitor.github.io/)
[2] https://damonitor.github.io/doc/html/latest/vm/damon/eval.html
[3] https://https://github.com/sjp38/linux/tree/damon/master (https://https//github.com/sjp38/linux/tree/damon/master)
[4] https://lore.kernel.org/linux-mm/20210520075629.4332-1-sj38.park@gmail.com/
[5] https://lore.kernel.org/linux-mm/20201216084404.23183-1-sjpark@amazon.com/
[6] https://lore.kernel.org/linux-mm/20201216094221.11898-1-sjpark@amazon.com/
[7] https://github.com/amazonlinux/linux/tree/amazon-5.4.y/master/mm/damon
[8] https://github.com/amazonlinux/linux/tree/amazon-5.10.y/master/mm/damon
[9] https://github.com/sjp38/linux/tree/damon/for-v5.4.y
[10] https://github.com/sjp38/linux/tree/damon/for-v5.10.y