On 8/13/24 12:56, 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.
Change-Id: Ib9dfc9004473baa6ef26ca7277d220b6199517de Signed-off-by: Yuanchu Xie yuanchu@google.com
Documentation/admin-guide/mm/index.rst | 1 + .../admin-guide/mm/workingset_report.rst | 105 ++++++++++++++++++
The new memory cgroup control files need to be documented in Documentation/admin-guide/cgroup-v2.rst as well.
Cheers, Longman
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 8b35795b664b..61a2a347fc91 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..ddcc0c33a8df --- /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_WORKINGSET_REPORT_AGING=y``
+Sysfs interfaces +================ +``/sys/devices/system/node/nodeX/workingset_report/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/workingset_report/page_age_intervals`` +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