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Commit 2a695ca4 authored by Mike Rapoport's avatar Mike Rapoport Committed by Jonathan Corbet
Browse files

docs/vm: ksm: update stable_node_chains_prune_millisecs description 



Make the description of stable_node_chains_prune_millisecs sysfs parameter
less implementation aware and add a few words about this parameter in the
"Design" section.

Signed-off-by: default avatarMike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent 6570c785

Documentation/vm/ksm.rst

+11 −8
Original line number Diff line number Diff line
@@ -150,14 +150,12 @@ max_page_sharing 
        traversals are always schedule friendly themselves.



stable_node_chains_prune_millisecs

        How frequently to walk the whole list of stable_node "dups"

        linked in the stable_node "chains" in order to prune stale

        stable_nodes. Smaller milllisecs values will free up the KSM

        metadata with lower latency, but they will make ksmd use more

        CPU during the scan. This only applies to the stable_node

        chains so it's a noop if not a single KSM page hit the

        ``max_page_sharing`` yet (there would be no stable_node chains in

        such case).

        specifies how frequently KSM checks the metadata of the pages

        that hit the deduplication limit for stale information.

        Smaller milllisecs values will free up the KSM metadata with

        lower latency, but they will make ksmd use more CPU during the

        scan. It's a noop if not a single KSM page hit the

        ``max_page_sharing`` yet.



The effectiveness of KSM and MADV_MERGEABLE is shown in ``/sys/kernel/mm/ksm/``:
@@ -249,6 +247,11 @@ deduplication factor at the expense of slower worst case for rmap 
walks for any KSM page which can happen during swapping, compaction,

NUMA balancing and page migration.



The whole list of stable_node "dups" linked in the stable_node

"chains" is scanned periodically in order to prune stale stable_nodes.

The frequency of such scans is defined by

``stable_node_chains_prune_millisecs`` sysfs tunable.



Reference

---------

.. kernel-doc:: mm/ksm.c