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Date: Tue, 24 Apr 2018 09:40:22 +0300 From: Mike Rapoport <rppt@...ux.vnet.ibm.com> To: Jonathan Corbet <corbet@....net> Cc: Andrew Morton <akpm@...ux-foundation.org>, Andrea Arcangeli <aarcange@...hat.com>, linux-doc <linux-doc@...r.kernel.org>, linux-mm <linux-mm@...ck.org>, lkml <linux-kernel@...r.kernel.org>, Mike Rapoport <rppt@...ux.vnet.ibm.com> Subject: [PATCH 1/7] 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: Mike Rapoport <rppt@...ux.vnet.ibm.com> --- mm/ksm.c | 19 ++++++++++++++++++- 1 file changed, 18 insertions(+), 1 deletion(-) diff --git a/mm/ksm.c b/mm/ksm.c index 58c2741..54155b1 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -51,7 +51,9 @@ #define DO_NUMA(x) do { } while (0) #endif -/* +/** + * DOC: Overview + * * A few notes about the KSM scanning process, * 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), * 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 * 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 -- 2.7.4
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