| Message ID | 20231218231054.1625219-5-shr@devkernel.io (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm/ksm: Add ksm advisor | expand |
Hi, On 12/18/23 15:10, Stefan Roesch wrote: > This documents the KSM advisor and its new knobs in /sys/fs/kernel/mm. > > Signed-off-by: Stefan Roesch <shr@devkernel.io> > Acked-by: David Hildenbrand <david@redhat.com> > --- > Documentation/admin-guide/mm/ksm.rst | 55 ++++++++++++++++++++++++++++ > 1 file changed, 55 insertions(+) > > diff --git a/Documentation/admin-guide/mm/ksm.rst b/Documentation/admin-guide/mm/ksm.rst > index e59231ac6bb71..a639cac124777 100644 > --- a/Documentation/admin-guide/mm/ksm.rst > +++ b/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 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. scan-time > + > 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. change > + > +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 scan-time > +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 I would drop to. aggressively > +important parameter for the configuration of the scan time advisor. scan-time > + > +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. recalculated > + > + > -- > Izik Eidus, > Hugh Dickins, 17 Nov 2009 thanks.
diff --git a/Documentation/admin-guide/mm/ksm.rst b/Documentation/admin-guide/mm/ksm.rst index e59231ac6bb71..a639cac124777 100644 --- a/Documentation/admin-guide/mm/ksm.rst +++ b/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