The patch titled
Subject: mm/ksm: document ksm advisor and its sysfs knobs
has been added to the -mm mm-unstable branch. Its filename is
mm-ksm-document-ksm-advisor-and-its-sysfs-knobs.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-ksm-document-ksm-advisor-and-its-sysfs-knobs.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Stefan Roesch <shr@xxxxxxxxxxxx>
Subject: mm/ksm: document ksm advisor and its sysfs knobs
Date: Mon, 18 Dec 2023 15:10:54 -0800
This documents the KSM advisor and its new knobs in /sys/fs/kernel/mm.
Link: https://lkml.kernel.org/r/20231218231054.1625219-5-shr@xxxxxxxxxxxx
Signed-off-by: Stefan Roesch <shr@xxxxxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/admin-guide/mm/ksm.rst | 55 +++++++++++++++++++++++++
1 file changed, 55 insertions(+)
--- a/Documentation/admin-guide/mm/ksm.rst~mm-ksm-document-ksm-advisor-and-its-sysfs-knobs
+++ a/Documentation/admin-guide/mm/ksm.rst
@@ -80,6 +80,9 @@ pages_to_scan
how many pages to scan before ksmd goes to sleep
e.g. ``echo 100 > /sys/kernel/mm/ksm/pages_to_scan``.
+ The pages_to_scan value cannot be changed if ``advisor_mode`` has
+ been set to scan-time.
+
Default: 100 (chosen for demonstration purposes)
sleep_millisecs
@@ -164,6 +167,29 @@ smart_scan
optimization is enabled. The ``pages_skipped`` metric shows how
effective the setting is.
+advisor_mode
+ The ``advisor_mode`` selects the current advisor. Two modes are
+ supported: none and scan-time. The default is none. By setting
+ ``advisor_mode`` to scan-time, the scan time advisor is enabled.
+ The section about ``advisor`` explains in detail how the scan time
+ advisor works.
+
+adivsor_max_cpu
+ specifies the upper limit of the cpu percent usage of the ksmd
+ background thread. The default is 70.
+
+advisor_target_scan_time
+ specifies the target scan time in seconds to scan all the candidate
+ pages. The default value is 200 seconds.
+
+advisor_min_pages_to_scan
+ specifies the lower limit of the ``pages_to_scan`` parameter of the
+ scan time advisor. The default is 500.
+
+adivsor_max_pages_to_scan
+ specifies the upper limit of the ``pages_to_scan`` parameter of the
+ scan time advisor. The default is 30000.
+
The effectiveness of KSM and MADV_MERGEABLE is shown in ``/sys/kernel/mm/ksm/``:
general_profit
@@ -263,6 +289,35 @@ ksm_swpin_copy
note that KSM page might be copied when swapping in because do_swap_page()
cannot do all the locking needed to reconstitute a cross-anon_vma KSM page.
+Advisor
+=======
+
+The number of candidate pages for KSM is dynamic. It can be often observed
+that during the startup of an application more candidate pages need to be
+processed. Without an advisor the ``pages_to_scan`` parameter needs to be
+sized for the maximum number of candidate pages. The scan time advisor can
+changes the ``pages_to_scan`` parameter based on demand.
+
+The advisor can be enabled, so KSM can automatically adapt to changes in the
+number of candidate pages to scan. Two advisors are implemented: none and
+scan-time. With none, no advisor is enabled. The default is none.
+
+The scan time advisor changes the ``pages_to_scan`` parameter based on the
+observed scan times. The possible values for the ``pages_to_scan`` parameter is
+limited by the ``advisor_max_cpu`` parameter. In addition there is also the
+``advisor_target_scan_time`` parameter. This parameter sets the target time to
+scan all the KSM candidate pages. The parameter ``advisor_target_scan_time``
+decides how aggressive the scan time advisor scans candidate pages. Lower
+values make the scan time advisor to scan more aggresively. This is the most
+important parameter for the configuration of the scan time advisor.
+
+The initial value and the maximum value can be changed with
+``advisor_min_pages_to_scan`` and ``advisor_max_pages_to_scan``. The default
+values are sufficient for most workloads and use cases.
+
+The ``pages_to_scan`` parameter is re-calculated after a scan has been completed.
+
+
--
Izik Eidus,
Hugh Dickins, 17 Nov 2009
_
Patches currently in -mm which might be from shr@xxxxxxxxxxxx are
mm-ksm-add-ksm-advisor.patch
mm-ksm-add-sysfs-knobs-for-advisor.patch
mm-ksm-add-tracepoint-for-ksm-advisor.patch
mm-ksm-document-ksm-advisor-and-its-sysfs-knobs.patch
