linux-kernel - [PATCH 1/1] mm/page_alloc: update comments in __free_pages

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Date:   Thu,  1 Dec 2022 21:50:45 +0800
From:   wonder_rock@....com
To:     akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Deyan Wang <wonder_rock@....com>
Subject: [PATCH 1/1] mm/page_alloc: update comments in __free_pages_ok()

From: Deyan Wang <wonder_rock@....com>

Add a comment to explain why we call get_pfnblock_migratetype() twice
in __free_pages_ok().

Signed-off-by: Deyan Wang <wonder_rock@....com>
---
 mm/page_alloc.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 2d4c81224508..52dd4fff280b 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1702,6 +1702,11 @@ static void __free_pages_ok(struct page *page, unsigned int order,
 	if (!free_pages_prepare(page, order, true, fpi_flags))
 		return;
 
+	/*
+	 * Calling get_pfnblock_migratetype() without spin_lock_irqsave() here
+	 * is used to avoid calling get_pfnblock_migratetype() under the lock.
+	 * This will reduce the lock holding time.
+	 */
 	migratetype = get_pfnblock_migratetype(page, pfn);
 
 	spin_lock_irqsave(&zone->lock, flags);
-- 
2.25.1