From: SeongJae Park <sjpark@xxxxxxxxx> On Fri, 11 Jun 2021 17:44:18 +0000 "Boehme, Markus" <markubo@xxxxxxxxx> wrote: > On Thu, 2021-05-20 at 07:56 +0000, SeongJae Park wrote: > > From: SeongJae Park <sjpark@xxxxxxxxx> > > > > This commit adds documents for DAMON under > > `Documentation/admin-guide/mm/damon/` and `Documentation/vm/damon/`. > > > > Signed-off-by: SeongJae Park <sjpark@xxxxxxxxx> > > --- > > 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 [...]
