linux-kernel - [PATCH] mm/memblock:use a more appropriate order calculation when free memblock pages

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Message-Id: <20201203152311.5272-1-carver4lio@163.com>
Date:   Thu,  3 Dec 2020 23:23:10 +0800
From:   carver4lio@....com
To:     rppt@...nel.org
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Hailong Liu <liu.hailong6@....com.cn>
Subject: [PATCH] mm/memblock:use a more appropriate order calculation when free memblock pages

From: Hailong Liu <liu.hailong6@....com.cn>

When system in the booting stage, pages span from [start, end] of a memblock
are freed to buddy in a order as large as possible (less than MAX_ORDER) at
first, then decrease gradually to a proper order(less than end) in a loop.

However, *min(MAX_ORDER - 1UL, __ffs(start))* can not get the largest order
in some cases.
Instead, *__ffs(end - start)* may be more appropriate and meaningful.

Signed-off-by: Hailong Liu <liu.hailong6@....com.cn>
---
 mm/memblock.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memblock.c b/mm/memblock.c
index b68ee8678..7c6d0dde7 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -1931,7 +1931,7 @@ static void __init __free_pages_memory(unsigned long start, unsigned long end)
 	int order;
 
 	while (start < end) {
-		order = min(MAX_ORDER - 1UL, __ffs(start));
+		order = min(MAX_ORDER - 1UL, __ffs(end - start));
 
 		while (start + (1UL << order) > end)
 			order--;
-- 
2.17.1