[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <82ea9158-c71e-4c11-a46d-397e9ec9349b@sk.com>
Date: Thu, 29 May 2025 16:21:39 +0900
From: Honggyu Kim <honggyu.kim@...com>
To: SeongJae Park <sj@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>
Cc: kernel_team@...ynix.com, Jonathan Corbet <corbet@....net>,
damon@...ts.linux.dev, kernel-team@...a.com, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 0/4] mm/damon: introduce DAMON_STAT for simple and
practical access monitoring
Hi SeongJae,
Thanks for your work.
On 5/27/2025 6:09 AM, SeongJae Park wrote:
> DAMON-based access monitoring is not simple due to required DAMON
> control and results visualizations. Introduce a static kernel module
> for making it simple. The module can be enabled without manual setup
> and provides access pattern metrics that easy to fetch and understand
> the practical access pattern information, namely estimated memory
> bandwidth and memory idle time percentiles.
>
> Background and Problems
> =======================
>
> DAMON can be used for monitoring data access patterns of the system and
> workloads. Specifically, users can start DAMON to monitor access events
> on specific address space with fine controls including address ranges to
> monitor and time intervals between samplings and aggregations. The
> resulting access information snapshot contains access frequency
> (nr_accesses) and how long the frequency was kept (age) for each byte.
>
> The monitoring usage is not simple and practical enough for production
> usage. Users should first start DAMON with a number of parameters, and
> wait until DAMON's monitoring results capture a reasonable amount of the
> time data (age). In production, such manual start and wait is
> impractical to capture useful information from a high number of machines
> in a timely manner.
>
> The monitoring result is also too detailed to be used on production
> environments. The raw results are hard to be aggregated and/or compared
> for production environments having a large scale of time, space and
> machines fleet.
>
> Users have to implement and use their own automation of DAMON control
> and results processing. It is repetitive and challenging since there is
> no good reference or guideline for such automation.
>
> Solution: DAMON_STAT
> ====================
>
> Implement such automation in kernel space as a static kernel module,
> namely DAMON_STAT. It can be enabled at build, boot, or run time via
> its build configuration or module parameter. It monitors the entire
> physical address space with monitoring intervals that auto-tuned for a
> reasonable amount of access observations and minimum overhead. It
> converts the raw monitoring results into simpler metrics that can easily
> be aggregated and compared, namely estimated memory bandwidth and idle
> time percentiles. Refer to the commit messages of the second and the
> third patches of this patch series for more details about the metrics.
I see the description looks good but it'd be useful if you could share some
execution commands and expected output examples that some newbies can get better
ideas.
I honestly do not have a clear idea how I can use this kind of static kernel
modules as general users although I have developed some features of DAMON.
So could you please help?
Thanks,
Honggyu
>
> Discussions
> ===========
>
> The module aims to be useful on production environments constructed with
> a large number of machines that run a long time. The auto-tuned
> monitoring intervals ensure a reasonable quality of the outputs. The
> auto-tuning also ensures its overhead be reasonable and low enough to be
> enabled always on the production. The simplified monitoring results
> metrics can be useful for showing both coldness (idle time percentiles)
> and hotness (memory bandwidth) of the system's access pattern. We
> expect the information can be useful for assessing system memory
> utilization and inspiring optimizations or investigations on both kernel
> and user space memory management logics for large scale fleets.
>
> We hence expect the module is good enough to be just used in most
> environments. For special cases that require a custom access monitoring
> automation, users will still benefit by using DAMON_STAT as a reference
> or a guideline for their specialized automation.
>
> Revision History
> ================
>
> Changes from RFC
> (https://lore.kernel.org/20250519164415.43935-1-sj@kernel.org)
> - Add an admin-guide documentation
> - Wordsmith commit messages
> - Rebase to latest mm-new
>
> SeongJae Park (4):
> mm/damon: introduce DAMON_STAT module
> mm/damon/stat: calculate and expose estimated memory bandwidth
> mm/damon/stat: calculate and expose idle time percentiles
> Docs/admin-guide/mm/damon: add DAMON_STAT usage document
>
> Documentation/admin-guide/mm/damon/index.rst | 1 +
> Documentation/admin-guide/mm/damon/stat.rst | 69 ++++++
> mm/damon/Kconfig | 16 ++
> mm/damon/Makefile | 1 +
> mm/damon/stat.c | 245 +++++++++++++++++++
> 5 files changed, 332 insertions(+)
> create mode 100644 Documentation/admin-guide/mm/damon/stat.rst
> create mode 100644 mm/damon/stat.c
>
>
> base-commit: 90887f57d7a67917136e7c70d26fb3f2fcdc6f53
Powered by blists - more mailing lists