linux-kernel - [PATCH v2] memblock: avoid some repeat when add new range

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Date:   Wed, 15 Jun 2022 17:40:15 +0800
From:   Jinyu Tang <tjytimi@....com>
To:     rppt@...nel.org
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Jinyu Tang <tjytimi@....com>
Subject: [PATCH v2] memblock: avoid some repeat when add new range

The worst case is that the new memory range overlaps all existing
regions,which need type->cnt + 1 free area of struct memblock_region.
So if type->cnt + 1 + type->cnt is less than type->max,we can insert
regions directly.And becase of merge operation in the end of function,
tpye->cnt increase slowly for many cases.So this patch can avoid
unnecessary repeat for many cases when add new memory range.

Signed-off-by: Jinyu Tang <tjytimi@....com>
---
V1 -> V2: 1.Change the code as reviewer suggestions
           2.Add comment in the code
           3.Move the code above the repeat lable, because if reapeat
           code executed twice, insert is already true and don't need
           to test

 mm/memblock.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/mm/memblock.c b/mm/memblock.c
index e4f03a6e8..e94661fd3 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -593,6 +593,17 @@ static int __init_memblock memblock_add_range(struct memblock_type *type,
 		type->total_size = size;
 		return 0;
 	}
+
+	/*
+	 * The max free regions needed is when new range overlaps all existing
+	 * regions, which will cost type->cnt + 1 free regions. So if
+	 * type->cnt * 2 + 1 is less than type->max, We can confirmed
+	 * that there is enough number of regions, and we can insert
+	 * regions directly.
+	 */
+	if (type->cnt * 2 + 1 < type->max)
+		insert = true;
+
 repeat:
 	/*
 	 * The following is executed twice.  Once with %false @insert and
-- 
2.30.2