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Message-Id: <20210611185308.10727-1-sjpark@amazon.de>
Date: Fri, 11 Jun 2021 18:53:08 +0000
From: SeongJae Park <sj38.park@...il.com>
To: "Boehme, Markus" <markubo@...zon.de>
Cc: "sj38.park@...il.com" <sj38.park@...il.com>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
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"greg@...ah.com" <greg@...ah.com>,
"linux-damon@...zon.com" <linux-damon@...zon.com>,
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Subject: Re: [PATCH v29 10/13] Documentation: Add documents for DAMON
From: SeongJae Park <sjpark@...zon.de>
On Fri, 11 Jun 2021 17:44:18 +0000 "Boehme, Markus" <markubo@...zon.de> wrote:
> On Thu, 2021-05-20 at 07:56 +0000, SeongJae Park wrote:
> > From: SeongJae Park <sjpark@...zon.de>
> >
> > This commit adds documents for DAMON under
> > `Documentation/admin-guide/mm/damon/` and `Documentation/vm/damon/`.
> >
> > Signed-off-by: SeongJae Park <sjpark@...zon.de>
> > ---
> > Documentation/admin-guide/mm/damon/guide.rst | 158 +++++++++++++
> > Documentation/admin-guide/mm/damon/index.rst | 15 ++
> > Documentation/admin-guide/mm/damon/plans.rst | 29 +++
> > Documentation/admin-guide/mm/damon/start.rst | 114 +++++++++
> > Documentation/admin-guide/mm/damon/usage.rst | 112 +++++++++
> > Documentation/admin-guide/mm/index.rst | 1 +
> > Documentation/vm/damon/api.rst | 20 ++
> > Documentation/vm/damon/design.rst | 166 +++++++++++++
> > Documentation/vm/damon/eval.rst | 232 +++++++++++++++++++
> > Documentation/vm/damon/faq.rst | 58 +++++
> > Documentation/vm/damon/index.rst | 31 +++
> > Documentation/vm/index.rst | 1 +
> > 12 files changed, 937 insertions(+)
> > create mode 100644 Documentation/admin-guide/mm/damon/guide.rst
> > create mode 100644 Documentation/admin-guide/mm/damon/index.rst
> > create mode 100644 Documentation/admin-guide/mm/damon/plans.rst
> > create mode 100644 Documentation/admin-guide/mm/damon/start.rst
> > create mode 100644 Documentation/admin-guide/mm/damon/usage.rst
> > create mode 100644 Documentation/vm/damon/api.rst
> > create mode 100644 Documentation/vm/damon/design.rst
> > create mode 100644 Documentation/vm/damon/eval.rst
> > create mode 100644 Documentation/vm/damon/faq.rst
> > create mode 100644 Documentation/vm/damon/index.rst
> >
> > [...]
> >
> > diff --git a/Documentation/admin-guide/mm/damon/start.rst b/Documentation/admin-guide/mm/damon/start.rst
> > new file mode 100644
> > index 000000000000..f5bbf1e36836
> > --- /dev/null
> > +++ b/Documentation/admin-guide/mm/damon/start.rst
> > @@ -0,0 +1,114 @@
> > +.. SPDX-License-Identifier: GPL-2.0
> > +
> > +===============
> > +Getting Started
> > +===============
> > +
> > +This document briefly describes how you can use DAMON by demonstrating its
> > +default user space tool. Please note that this document describes only a part
> > +of its features for brevity. Please refer to :doc:`usage` for more details.
> > [...]
> > +
> > +
> > +Prerequisites
> > +=============
> > +
> > +Kernel
> > +------
> > +
> > +You should first ensure your system is running on a kernel built with
> > +``CONFIG_DAMON_*=y``.
> > +
> > +
> > +User Space Tool
> > +---------------
> > +
> > +For the demonstration, we will use the default user space tool for DAMON,
> > +called DAMON Operator (DAMO). It is available at
> > +https://github.com/awslabs/damo. For brevity, below examples assume you set
> > +``$PATH`` to point it. It's not mandatory, though.
>
> "The examples below assume ``damo`` is on your ``$PATH``."?
That's much better for readability. I will update so in the next spin.
>
> > +
> > +Because DAMO is using the debugfs interface (refer to :doc:`usage` for the
> > +detail) of DAMON, you should ensure debugfs is mounted. Mount it manually as
> > +below::
> > +
> > + # mount -t debugfs none /sys/kernel/debug/
> > +
> > +or append below line to your ``/etc/fstab`` file so that your system can
> > +automatically mount debugfs from next booting::
> > +
> > + debugfs /sys/kernel/debug debugfs defaults 0 0
> > +
> > +
> > [...]
> > diff --git a/Documentation/admin-guide/mm/damon/usage.rst b/Documentation/admin-guide/mm/damon/usage.rst
> > new file mode 100644
> > index 000000000000..ea3fa6e55f8b
> > --- /dev/null
> > +++ b/Documentation/admin-guide/mm/damon/usage.rst
> > @@ -0,0 +1,112 @@
> > +.. SPDX-License-Identifier: GPL-2.0
> > +
> > +===============
> > +Detailed Usages
> > +===============
> > [...]
> > +
> > +Tracepoint for Monitoring Results
> > +=================================
> > +
> > +DAMON provides the monitoring results via a tracepoint,
> > +``damon:damon_aggregated``. While the monitoring is turned on, you could
> > +record the tracepoint events and show results using tracepoint supporting tools
> > +like ``perf``. For example::
> > +
> > + # echo on > monitor_on
> > + # perf record damon:damon_aggregated &
>
> I think that needs to be "-e damon:damon_aggregated".
Good catch, I will fix in the next spin!
>
> > + # sleep 5
> > + # kill 9 $(pidof perf)
> > + # echo off > monitor_on
> > + # perf script
> >
> > [...]
> >
> > diff --git a/Documentation/vm/damon/design.rst b/Documentation/vm/damon/design.rst
> > new file mode 100644
> > index 000000000000..727d72093f8f
> > --- /dev/null
> > +++ b/Documentation/vm/damon/design.rst
> > @@ -0,0 +1,166 @@
> > +.. SPDX-License-Identifier: GPL-2.0
> > +
> > +======
> > +Design
> > +======
> > +
> > [...]
> > +
> > +Reference Implementations of Address Space Specific Primitives
> > +==============================================================
> > +
> > +The low level primitives for the fundamental access monitoring are defined in
> > +two parts:
> > +
> > +1. Identification of the monitoring target address range for the address space.
> > +2. Access check of specific address range in the target space.
> > +
> > +DAMON currently provides the implementation of the primitives for only the
> > +virtual address spaces. Below two subsections describe how it works.
> > +
> > +
> > +PTE Accessed-bit Based Access Check
> > +-----------------------------------
> > +
> > +The implementation for the virtual address space uses PTE Accessed-bit for
> > +basic access checks. It finds the relevant PTE Accessed bit from the address
> > +by walking the page table for the target task of the address. In this way, the
> > +implementation finds and clears the bit for next sampling target address and
> > +checks whether the bit set again after one sampling period. This could disturb
> > +other kernel subsystems using the Accessed bits, namely Idle page tracking and
> > +the reclaim logic. To avoid such disturbances, DAMON makes it mutually
> > +exclusive with Idle page tracking and uses ``PG_idle`` and ``PG_young`` page
> > +flags to solve the conflict with the reclaim logic, as Idle page tracking does.
> > +
> > +
> > +VMA-based Target Address Range Construction
> > +-------------------------------------------
> > +
> > +Only small parts in the super-huge virtual address space of the processes are
> > +mapped to the physical memory and accessed. Thus, tracking the unmapped
> > +address regions is just wasteful. However, because DAMON can deal with some
> > +level of noise using the adaptive regions adjustment mechanism, tracking every
> > +mapping is not strictly required but could even incur a high overhead in some
> > +cases. That said, too huge unmapped areas inside the monitoring target should
> > +be removed to not take the time for the adaptive mechanism.
> > +
> > +For the reason, this implementation converts the complex mappings to three
> > +distinct regions that cover every mapped area of the address space. The two
> > +gaps between the three regions are the two biggest unmapped areas in the given
> > +address space. The two biggest unmapped areas would be the gap between the
> > +heap and the uppermost mmap()-ed region, and the gap between the lowermost
> > +mmap()-ed region and the stack in most of the cases. Because these gaps are
> > +exceptionally huge in usual address spaces, excluding these will be sufficient
> > +to make a reasonable trade-off. Below shows this in detail::
> > +
> > + <heap>
> > + <BIG UNMAPPED REGION 1>
> > + <uppermost mmap()-ed region>
> > + (small mmap()-ed regions and munmap()-ed regions)
> > + <lowermost mmap()-ed region>
> > + <BIG UNMAPPED REGION 2>
> > + <stack>
> > +
>
> Nit: I'd swap these sections so they match the ordered list in the
> section overview.
Good point! I will do so in the next spin!
>
> > [...]
>
> I skipped the files you mentioned would be dropped from the next
> revision.
Thanks, hope it didn't distracted you.
Thanks,
SeongJae Park
[...]
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