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docs/vm: ksm: udpate description of stable_node_{dups,chains} 

Remove implementation details from sysfs parameter descriptions.
Also move the paragraph discussing fragmentation issues and their possible
solution to 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 09:40:27 +03:00 committed by Jonathan Corbet
parent 2a695ca412
commit 8b898fd114
1 changed files with 10 additions and 11 deletions
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21
Documentation/vm/ksm.rst
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@ -170,10 +170,9 @@ pages_volatile
full_scans
how many times all mergeable areas have been scanned
stable_node_chains
number of stable node chains allocated, this is effectively
the number of KSM pages that hit the ``max_page_sharing`` limit
stable_node_dups
number of stable node dups queued into the stable_node chains
number of duplicated KSM pages
A high ratio of ``pages_sharing`` to ``pages_shared`` indicates good
sharing, but a high ratio of ``pages_unshared`` to ``pages_sharing``
@ -185,15 +184,6 @@ The maximum possible ``pages_sharing/pages_shared`` ratio is limited by the
``max_page_sharing`` tunable. To increase the ratio ``max_page_sharing`` must
be increased accordingly.
The ``stable_node_dups/stable_node_chains`` ratio is also affected by the
``max_page_sharing`` tunable, and an high ratio may indicate fragmentation
in the stable_node dups, which could be solved by introducing
fragmentation algorithms in ksmd which would refile rmap_items from
one stable_node dup to another stable_node dup, in order to free up
stable_node "dups" with few rmap_items in them, but that may increase
the ksmd CPU usage and possibly slowdown the readonly computations on
the KSM pages of the applications.
Design
======
@ -247,6 +237,15 @@ 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 ``stable_node_dups/stable_node_chains`` ratio is also affected by the
``max_page_sharing`` tunable, and an high ratio may indicate fragmentation
in the stable_node dups, which could be solved by introducing
fragmentation algorithms in ksmd which would refile rmap_items from
one stable_node dup to another stable_node dup, in order to free up
stable_node "dups" with few rmap_items in them, but that may increase
the ksmd CPU usage and possibly slowdown the readonly computations on
the KSM pages of the applications.
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