This documents the KSM advisor and its new knobs in /sys/fs/kernel/mm.
Signed-off-by: Stefan Roesch <shr@xxxxxxxxxxxx>
---
Documentation/admin-guide/mm/ksm.rst | 45 ++++++++++++++++++++++++++++
1 file changed, 45 insertions(+)
diff --git a/Documentation/admin-guide/mm/ksm.rst b/Documentation/admin-guide/mm/ksm.rst
index e59231ac6bb7..8de93650d3b0 100644
--- a/Documentation/admin-guide/mm/ksm.rst
+++ b/Documentation/admin-guide/mm/ksm.rst
@@ -164,6 +164,25 @@ 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: 0 (None) and 1 (Scan time). The default is None. By
+ setting ``advisor_mode`` to 1, the scan time advisor is enabled.
+ The section about ``advisor`` explains in detail how the scan time
+ advisor works.
+
+advisor_min_pages
+ specifies the lower limit of the ``pages_to_scan`` parameter of the
+ scan time advisor. The default is 500.
+
+adivsor_max_pages
+ specifies the upper limit of the ``pages_to_scan`` parameter of the
+ scan time advisor. The default is 5000.
+
+advisor_target_scan_time
+ specifies the target scan time in seconds to scan all the candidate
+ pages. The default value is 200 seconds.
+
The effectiveness of KSM and MADV_MERGEABLE is shown in ``/sys/kernel/mm/ksm/``:
general_profit
@@ -263,6 +282,32 @@ 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: 0 (None) and
+1 (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_min_pages`` and ``advisor_max_pages`` parameters. 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 ``pages_to_scan`` parameter is re-calculated after a scan has been completed.
+
+
--
Izik Eidus,
Hugh Dickins, 17 Nov 2009
--
2.39.3
