+ maple_tree-optimize-mas_wr_append-also-improve-duplicating-vmas.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: maple_tree: optimize mas_wr_append(), also improve duplicating VMAs
has been added to the -mm mm-unstable branch.  Its filename is
     maple_tree-optimize-mas_wr_append-also-improve-duplicating-vmas.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/maple_tree-optimize-mas_wr_append-also-improve-duplicating-vmas.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Peng Zhang <zhangpeng.00@bytedance.com>
Subject: maple_tree: optimize mas_wr_append(), also improve duplicating VMAs
Date: Wed, 28 Jun 2023 15:36:56 +0800

When the new range can be completely covered by the original last range
without touching the boundaries on both sides, two new entries can be
appended to the end as a fast path. We update the original last pivot at
the end, and the newly appended two entries will not be accessed before
this, so it is also safe in RCU mode.

This is useful for sequential insertion, which is what we do in
dup_mmap(). Enabling BENCH_FORK in test_maple_tree and just running
bench_forking() gives the following time-consuming numbers:

before:               after:
17,874.83 msec        15,738.38 msec

It shows about a 12% performance improvement for duplicating VMAs.

Link: https://lkml.kernel.org/r/20230628073657.75314-4-zhangpeng.00@bytedance.com
Signed-off-by: Peng Zhang <zhangpeng.00@bytedance.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 lib/maple_tree.c |   33 ++++++++++++++++++++++-----------
 1 file changed, 22 insertions(+), 11 deletions(-)

--- a/lib/maple_tree.c~maple_tree-optimize-mas_wr_append-also-improve-duplicating-vmas
+++ a/lib/maple_tree.c
@@ -4266,10 +4266,10 @@ static inline unsigned char mas_wr_new_e
  *
  * Return: True if appended, false otherwise
  */
-static inline bool mas_wr_append(struct ma_wr_state *wr_mas)
+static inline bool mas_wr_append(struct ma_wr_state *wr_mas,
+				 unsigned char new_end)
 {
 	unsigned char end = wr_mas->node_end;
-	unsigned char new_end = end + 1;
 	struct ma_state *mas = wr_mas->mas;
 	unsigned char node_pivots = mt_pivots[wr_mas->type];
 
@@ -4281,16 +4281,27 @@ static inline bool mas_wr_append(struct
 		ma_set_meta(wr_mas->node, maple_leaf_64, 0, new_end);
 	}
 
-	if (mas->last == wr_mas->r_max) {
-		/* Append to end of range */
-		rcu_assign_pointer(wr_mas->slots[new_end], wr_mas->entry);
-		wr_mas->pivots[end] = mas->index - 1;
-		mas->offset = new_end;
+	if (new_end == wr_mas->node_end + 1) {
+		if (mas->last == wr_mas->r_max) {
+			/* Append to end of range */
+			rcu_assign_pointer(wr_mas->slots[new_end],
+					   wr_mas->entry);
+			wr_mas->pivots[end] = mas->index - 1;
+			mas->offset = new_end;
+		} else {
+			/* Append to start of range */
+			rcu_assign_pointer(wr_mas->slots[new_end],
+					   wr_mas->content);
+			wr_mas->pivots[end] = mas->last;
+			rcu_assign_pointer(wr_mas->slots[end], wr_mas->entry);
+		}
 	} else {
-		/* Append to start of range */
+		/* Append to the range without touching any boundaries. */
 		rcu_assign_pointer(wr_mas->slots[new_end], wr_mas->content);
-		wr_mas->pivots[end] = mas->last;
-		rcu_assign_pointer(wr_mas->slots[end], wr_mas->entry);
+		wr_mas->pivots[end + 1] = mas->last;
+		rcu_assign_pointer(wr_mas->slots[end + 1], wr_mas->entry);
+		wr_mas->pivots[end] = mas->index - 1;
+		mas->offset = end + 1;
 	}
 
 	if (!wr_mas->content || !wr_mas->entry)
@@ -4337,7 +4348,7 @@ static inline void mas_wr_modify(struct
 		goto slow_path;
 
 	/* Attempt to append */
-	if (new_end == wr_mas->node_end + 1 && mas_wr_append(wr_mas))
+	if (mas_wr_append(wr_mas, new_end))
 		return;
 
 	if (new_end == wr_mas->node_end && mas_wr_slot_store(wr_mas))
_

Patches currently in -mm which might be from zhangpeng.00@bytedance.com are

maple_tree-add-test-for-mas_wr_modify-fast-path.patch
maple_tree-add-test-for-expanding-range-in-rcu-mode.patch
maple_tree-optimize-mas_wr_append-also-improve-duplicating-vmas.patch
maple_tree-add-a-fast-path-case-in-mas_wr_slot_store.patch