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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: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Mike Rapoport 2018-04-24 09:40:26 +03:00 committed by Jonathan Corbet
parent 6570c785ea
commit 2a695ca412
1 changed files with 11 additions and 8 deletions
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19
Documentation/vm/ksm.rst
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@ -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