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Commit 8b898fd1 authored by Mike Rapoport's avatar Mike Rapoport Committed by Jonathan Corbet
Browse files

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: default avatarMike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent 2a695ca4

Documentation/vm/ksm.rst

+10 −11
Original line number Diff line number Diff line
@@ -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