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

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

mm/ksm.c

+18 −1
Original line number Original line Diff line number Diff line
@@ -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 @@ 
 * 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