linux-kernel - [PATCH] mm/hugetlb: remove unnecessary memory fetch in PageHeadHuge()

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Message-Id: <20200311172440.6988-1-vbabka@suse.cz>
Date:   Wed, 11 Mar 2020 18:24:40 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Mike Kravetz <mike.kravetz@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCH] mm/hugetlb: remove unnecessary memory fetch in PageHeadHuge()

Commit f1e61557f023 ("mm: pack compound_dtor and compound_order into one word
in struct page") changed compound_dtor from a pointer to an array index in
order to pack it. To check if page has the hugeltbfs compound_dtor, we can
just compare the index directly without fetching the function pointer.
Said commit did that with PageHuge() and we can do the same with PageHeadHuge()
to make the code a bit smaller and faster.

Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
Cc: Mike Kravetz <mike.kravetz@...cle.com>
Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
---
 mm/hugetlb.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index dd8737a94bec..ba1ca452aa7f 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1313,7 +1313,7 @@ int PageHeadHuge(struct page *page_head)
 	if (!PageHead(page_head))
 		return 0;
 
-	return get_compound_page_dtor(page_head) == free_huge_page;
+	return page_head[1].compound_dtor == HUGETLB_PAGE_DTOR;
 }
 
 pgoff_t __basepage_index(struct page *page)
-- 
2.25.1