Commit 5a2ca3ef authored by Mike Rapoport's avatar Mike Rapoport Committed by Jonathan Corbet

mm/ksm: docs: extend overview comment and make it "DOC:"

The existing comment provides a good overview of KSM implementation. Let's
update it to reflect recent additions of "chain" and "dup" variants of the
stable tree nodes and mark it as "DOC:" for inclusion into the KSM
documentation.
Signed-off-by: default avatarMike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent b976583f
...@@ -51,7 +51,9 @@ ...@@ -51,7 +51,9 @@
#define DO_NUMA(x) do { } while (0) #define DO_NUMA(x) do { } while (0)
#endif #endif
/* /**
* DOC: Overview
*
* A few notes about the KSM scanning process, * A few notes about the KSM scanning process,
* to make it easier to understand the data structures below: * to make it easier to understand the data structures below:
* *
...@@ -67,6 +69,21 @@ ...@@ -67,6 +69,21 @@
* this tree is fully assured to be working (except when pages are unmapped), * this tree is fully assured to be working (except when pages are unmapped),
* and therefore this tree is called the stable tree. * and therefore this tree is called the stable tree.
* *
* The stable tree node includes information required for reverse
* mapping from a KSM page to virtual addresses that map this page.
*
* In order to avoid large latencies of the rmap walks on KSM pages,
* KSM maintains two types of nodes in the stable tree:
*
* * the regular nodes that keep the reverse mapping structures in a
* linked list
* * the "chains" that link nodes ("dups") that represent the same
* write protected memory content, but each "dup" corresponds to a
* different KSM page copy of that content
*
* Internally, the regular nodes, "dups" and "chains" are represented
* using the same :c:type:`struct stable_node` structure.
*
* In addition to the stable tree, KSM uses a second data structure called the * In addition to the stable tree, KSM uses a second data structure called the
* unstable tree: this tree holds pointers to pages which have been found to * unstable tree: this tree holds pointers to pages which have been found to
* be "unchanged for a period of time". The unstable tree sorts these pages * be "unchanged for a period of time". The unstable tree sorts these pages
......
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