linux-kernel - [PATCH v2] mm/page_alloc: minor clean up for memmap_init

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Date:   Sat, 11 Jun 2022 10:13:52 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     <akpm@...ux-foundation.org>
CC:     <joao.m.martins@...cle.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, <linmiaohe@...wei.com>
Subject: [PATCH v2] mm/page_alloc: minor clean up for memmap_init_compound()

Since commit 5232c63f46fd ("mm: Make compound_pincount always available"),
compound_pincount_ptr is stored at first tail page now. So we should call
prep_compound_head() after the first tail page is initialized to take
advantage of the likelihood of that tail struct page being cached given
that we will read them right after in prep_compound_head().

Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
Cc: Joao Martins <joao.m.martins@...cle.com>
---
v2:
  Don't move prep_compound_head() outside loop per Joao.
---
 mm/page_alloc.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 4c7d99ee58b4..048df5d78add 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6771,13 +6771,18 @@ static void __ref memmap_init_compound(struct page *head,
 		set_page_count(page, 0);
 
 		/*
-		 * The first tail page stores compound_mapcount_ptr() and
-		 * compound_order() and the second tail page stores
-		 * compound_pincount_ptr(). Call prep_compound_head() after
-		 * the first and second tail pages have been initialized to
-		 * not have the data overwritten.
+		 * The first tail page stores compound_mapcount_ptr(),
+		 * compound_order() and compound_pincount_ptr(). Call
+		 * prep_compound_head() after the first tail page have
+		 * been initialized to not have the data overwritten.
+		 *
+		 * Note the idea to make this right after we initialize
+		 * the offending tail pages is trying to take advantage
+		 * of the likelihood of those tail struct pages being
+		 * cached given that we will read them right after in
+		 * prep_compound_head().
 		 */
-		if (pfn == head_pfn + 2)
+		if (unlikely(pfn == head_pfn + 1))
 			prep_compound_head(head, order);
 	}
 }
-- 
2.23.0