diff mbox series

[v2,8/8] Docs/admin-guide/mm/workingset_report: document sysfs and memcg interfaces

Message ID 20240604020549.1017540-9-yuanchu@google.com
State Superseded
Headers show
Series mm: workingset reporting | expand

Commit Message

Yuanchu Xie June 4, 2024, 2:05 a.m. UTC
Add workingset reporting documentation for better discoverability of
its sysfs and memcg interfaces. Also document the required kernel
config to enable workingset reporting.

Signed-off-by: Yuanchu Xie <yuanchu@google.com>
---
 Documentation/admin-guide/mm/index.rst        |   1 +
 .../admin-guide/mm/workingset_report.rst      | 105 ++++++++++++++++++
 2 files changed, 106 insertions(+)
 create mode 100644 Documentation/admin-guide/mm/workingset_report.rst

Comments

Randy Dunlap June 6, 2024, 5:02 p.m. UTC | #1
Hi,

Just a couple of nits below:

On 6/3/24 7:05 PM, Yuanchu Xie wrote:
> Add workingset reporting documentation for better discoverability of
> its sysfs and memcg interfaces. Also document the required kernel
> config to enable workingset reporting.
> 
> Signed-off-by: Yuanchu Xie <yuanchu@google.com>
> ---
>  Documentation/admin-guide/mm/index.rst        |   1 +
>  .../admin-guide/mm/workingset_report.rst      | 105 ++++++++++++++++++
>  2 files changed, 106 insertions(+)
>  create mode 100644 Documentation/admin-guide/mm/workingset_report.rst
> 
> diff --git a/Documentation/admin-guide/mm/index.rst b/Documentation/admin-guide/mm/index.rst
> index 1f883abf3f00..fba987de8997 100644
> --- a/Documentation/admin-guide/mm/index.rst
> +++ b/Documentation/admin-guide/mm/index.rst
> @@ -41,4 +41,5 @@ the Linux memory management.
>     swap_numa
>     transhuge
>     userfaultfd
> +   workingset_report
>     zswap
> diff --git a/Documentation/admin-guide/mm/workingset_report.rst b/Documentation/admin-guide/mm/workingset_report.rst
> new file mode 100644
> index 000000000000..f455ae93b30e
> --- /dev/null
> +++ b/Documentation/admin-guide/mm/workingset_report.rst
> @@ -0,0 +1,105 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +=================
> +Workingset Report
> +=================
> +Workingset report provides a view of memory coldness in user-defined
> +time intervals, i.e. X bytes are Y milliseconds cold. It breaks down
> +the user pages in the system per-NUMA node, per-memcg, for both
> +anonymous and file pages into histograms that look like:
> +::
> +
> +    1000 anon=137368 file=24530
> +    20000 anon=34342 file=0
> +    30000 anon=353232 file=333608
> +    40000 anon=407198 file=206052
> +    9223372036854775807 anon=4925624 file=892892
> +
> +The workingset reports can be used to drive proactive reclaim, by
> +identifying the number of cold bytes in a memcg, then writing to
> +``memory.reclaim``.
> +
> +Quick start
> +===========
> +Build the kernel with the following configurations. The report relies
> +on Multi-gen LRU for page coldness.
> +
> +* ``CONFIG_LRU_GEN=y``
> +* ``CONFIG_LRU_GEN_ENABLED=y``
> +* ``CONFIG_WORKINGSET_REPORT=y``
> +
> +Optionally, the aging kernel daemon can be enabled with the following
> +configuration.
> +* ``CONFIG_LRU_GEN_ENABLED=y``
> +
> +Sysfs interfaces
> +================
> +``/sys/devices/system/node/nodeX/page_age`` provides a per-node page
> +age histogram, showing an aggregate of the node's lruvecs.
> +Reading this file causes a hierarchical aging of all lruvecs, scanning
> +pages and creates a new Multi-gen LRU generation in each lruvec.
> +For example:
> +::
> +
> +    1000 anon=0 file=0
> +    2000 anon=0 file=0
> +    100000 anon=5533696 file=5566464
> +    18446744073709551615 anon=0 file=0
> +
> +``/sys/devices/system/node/nodeX/page_age_interval`` is a comma
> +separated list of time in milliseconds that configures what the page
> +age histogram uses for aggregation. For the above histogram,
> +the intervals are:
> +::
> +    1000,2000,100000
> +
> +``/sys/devices/system/node/nodeX/workingset_report/refresh_interval``
> +defines the amount of time the report is valid for in milliseconds.
> +When a report is still valid, reading the ``page_age`` file shows
> +the existing valid report, instead of generating a new one.
> +
> +``/sys/devices/system/node/nodeX/workingset_report/report_threshold``
> +specifies how often the userspace agent can be notified for node
> +memory pressure, in milliseconds. When a node reaches its low
> +watermarks and wakes up kswapd, programs waiting on ``page_age`` are
> +woken up so they can read the histogram and make policy decisions.
> +
> +Memcg interface
> +===============
> +While ``page_age_interval`` is defined per-node in sysfs. ``page_age``,

                                                      sysfs,

> +``refresh_interval`` and ``report_threshold`` are available per-memcg.
> +
> +``/sys/fs/cgroup/.../memory.workingset.page_age``
> +The memcg equivalent of the sysfs workingset page age histogram,

                                                       no comma   ^

> +breaks down the workingset of this memcg and its children into
> +page age intervals. Each node is prefixed with a node header and
> +a newline. Non-proactive direct reclaim on this memcg can also
> +wake up userspace agents that are waiting on this file.
> +e.g.
> +::
> +
> +    N0
> +    1000 anon=0 file=0
> +    2000 anon=0 file=0
> +    3000 anon=0 file=0
> +    4000 anon=0 file=0
> +    5000 anon=0 file=0
> +    18446744073709551615 anon=0 file=0
> +
> +``/sys/fs/cgroup/.../memory.workingset.refresh_interval``
> +The memcg equivalent of the sysfs refresh interval. A per-node
> +number of how much time a page age histogram is valid for, in
> +milliseconds.
> +e.g.
> +::
> +
> +    echo N0=2000 > memory.workingset.refresh_interval
> +
> +``/sys/fs/cgroup/.../memory.workingset.report_threshold``
> +The memcg equivalent of the sysfs report threshold. A per-node
> +number of how often userspace agent waiting on the page age
> +histogram can be woken up, in milliseconds.
> +e.g.
> +::
> +
> +    echo N0=1000 > memory.workingset.report_threshold
diff mbox series

Patch

diff --git a/Documentation/admin-guide/mm/index.rst b/Documentation/admin-guide/mm/index.rst
index 1f883abf3f00..fba987de8997 100644
--- a/Documentation/admin-guide/mm/index.rst
+++ b/Documentation/admin-guide/mm/index.rst
@@ -41,4 +41,5 @@  the Linux memory management.
    swap_numa
    transhuge
    userfaultfd
+   workingset_report
    zswap
diff --git a/Documentation/admin-guide/mm/workingset_report.rst b/Documentation/admin-guide/mm/workingset_report.rst
new file mode 100644
index 000000000000..f455ae93b30e
--- /dev/null
+++ b/Documentation/admin-guide/mm/workingset_report.rst
@@ -0,0 +1,105 @@ 
+.. SPDX-License-Identifier: GPL-2.0
+
+=================
+Workingset Report
+=================
+Workingset report provides a view of memory coldness in user-defined
+time intervals, i.e. X bytes are Y milliseconds cold. It breaks down
+the user pages in the system per-NUMA node, per-memcg, for both
+anonymous and file pages into histograms that look like:
+::
+
+    1000 anon=137368 file=24530
+    20000 anon=34342 file=0
+    30000 anon=353232 file=333608
+    40000 anon=407198 file=206052
+    9223372036854775807 anon=4925624 file=892892
+
+The workingset reports can be used to drive proactive reclaim, by
+identifying the number of cold bytes in a memcg, then writing to
+``memory.reclaim``.
+
+Quick start
+===========
+Build the kernel with the following configurations. The report relies
+on Multi-gen LRU for page coldness.
+
+* ``CONFIG_LRU_GEN=y``
+* ``CONFIG_LRU_GEN_ENABLED=y``
+* ``CONFIG_WORKINGSET_REPORT=y``
+
+Optionally, the aging kernel daemon can be enabled with the following
+configuration.
+* ``CONFIG_LRU_GEN_ENABLED=y``
+
+Sysfs interfaces
+================
+``/sys/devices/system/node/nodeX/page_age`` provides a per-node page
+age histogram, showing an aggregate of the node's lruvecs.
+Reading this file causes a hierarchical aging of all lruvecs, scanning
+pages and creates a new Multi-gen LRU generation in each lruvec.
+For example:
+::
+
+    1000 anon=0 file=0
+    2000 anon=0 file=0
+    100000 anon=5533696 file=5566464
+    18446744073709551615 anon=0 file=0
+
+``/sys/devices/system/node/nodeX/page_age_interval`` is a comma
+separated list of time in milliseconds that configures what the page
+age histogram uses for aggregation. For the above histogram,
+the intervals are:
+::
+    1000,2000,100000
+
+``/sys/devices/system/node/nodeX/workingset_report/refresh_interval``
+defines the amount of time the report is valid for in milliseconds.
+When a report is still valid, reading the ``page_age`` file shows
+the existing valid report, instead of generating a new one.
+
+``/sys/devices/system/node/nodeX/workingset_report/report_threshold``
+specifies how often the userspace agent can be notified for node
+memory pressure, in milliseconds. When a node reaches its low
+watermarks and wakes up kswapd, programs waiting on ``page_age`` are
+woken up so they can read the histogram and make policy decisions.
+
+Memcg interface
+===============
+While ``page_age_interval`` is defined per-node in sysfs. ``page_age``,
+``refresh_interval`` and ``report_threshold`` are available per-memcg.
+
+``/sys/fs/cgroup/.../memory.workingset.page_age``
+The memcg equivalent of the sysfs workingset page age histogram,
+breaks down the workingset of this memcg and its children into
+page age intervals. Each node is prefixed with a node header and
+a newline. Non-proactive direct reclaim on this memcg can also
+wake up userspace agents that are waiting on this file.
+e.g.
+::
+
+    N0
+    1000 anon=0 file=0
+    2000 anon=0 file=0
+    3000 anon=0 file=0
+    4000 anon=0 file=0
+    5000 anon=0 file=0
+    18446744073709551615 anon=0 file=0
+
+``/sys/fs/cgroup/.../memory.workingset.refresh_interval``
+The memcg equivalent of the sysfs refresh interval. A per-node
+number of how much time a page age histogram is valid for, in
+milliseconds.
+e.g.
+::
+
+    echo N0=2000 > memory.workingset.refresh_interval
+
+``/sys/fs/cgroup/.../memory.workingset.report_threshold``
+The memcg equivalent of the sysfs report threshold. A per-node
+number of how often userspace agent waiting on the page age
+histogram can be woken up, in milliseconds.
+e.g.
+::
+
+    echo N0=1000 > memory.workingset.report_threshold