maple_tree: introduce maple_copy node and use it in mas_spanning_rebalance()

Introduce an internal-memory only node type called maple_copy to
facilitate internal copy operations.  Use it in mas_spanning_rebalance()
for just the leaf nodes.  Initially, the maple_copy node is used to
configure the source nodes and copy the data into the big_node.

The maple_copy contains a list of source entries with start and end
offsets.  One of the maple_copy entries can be itself with an offset of 0
to 2, representing the data where the store partially overwrites entries,
or fully overwrites the entry.  The side effect is that the source nodes
no longer have to worry about partially copying the existing offset if it
is not fully overwritten.

This is in preparation of removal of the maple big_node, but for the time
being the data is copied to the big node to limit the change size.

Link: https://lkml.kernel.org/r/20260130205935.2559335-12-Liam.Howlett@oracle.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Andrew Ballance <andrewjballance@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Christian Kujau <lists@nerdbynature.de>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: SeongJae Park <sj@kernel.org>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 26 insertions, 0 deletions

diff --git a/include/linux/maple_tree.h b/include/linux/maple_tree.h
index 7b8aad47121e..9bc7fa89bc2e 100644
--- a/include/linux/maple_tree.h
+++ b/include/linux/maple_tree.h
@@ -139,6 +139,7 @@ enum maple_type {
 	maple_leaf_64,
 	maple_range_64,
 	maple_arange_64,
+	maple_copy,
 };
 
 enum store_type {
@@ -154,6 +155,30 @@ enum store_type {
 	wr_slot_store,
 };
 
+struct maple_copy {
+	struct {
+		struct maple_node *node;
+		unsigned long max;
+		unsigned char start;
+		unsigned char end;
+		enum maple_type mt;
+	} src[4];
+	/* Simulated node */
+	void __rcu *slot[3];
+	unsigned long min;
+	union {
+		unsigned long pivot[3];
+		struct {
+			void *_pad[2];
+			unsigned long max;
+		};
+	};
+	unsigned char end;
+
+	/*Avoid passing these around */
+	unsigned char s_count;
+};
+
 /**
  * DOC: Maple tree flags
  *
@@ -299,6 +324,7 @@ struct maple_node {
 		};
 		struct maple_range_64 mr64;
 		struct maple_arange_64 ma64;
+		struct maple_copy cp;
 	};
 };