linux-kernel - [PATCH 02/11] PageSlab: eliminate unnecessary compound

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Message-Id: <20211012180148.1669685-3-hannes@cmpxchg.org>
Date:   Tue, 12 Oct 2021 14:01:39 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     linux-mm@...ck.org
Cc:     Matthew Wilcox <willy@...radead.org>,
        Kent Overstreet <kent.overstreet@...il.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...e.com>, Roman Gushchin <guro@...com>,
        linux-kernel@...r.kernel.org, kernel-team@...com
Subject: [PATCH 02/11] PageSlab: eliminate unnecessary compound_head() calls in fs/proc/page

Cache multiple lookups in a local variable.

Signed-off-by: Johannes Weiner <hannes@...xchg.org>
---
 fs/proc/page.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/proc/page.c b/fs/proc/page.c
index 2c249f84e1fd..37d95309e1c1 100644
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -108,6 +108,7 @@ static inline u64 kpf_copy_bit(u64 kflags, int ubit, int kbit)
 
 u64 stable_page_flags(struct page *page)
 {
+	struct page *head;
 	u64 k;
 	u64 u;
 
@@ -118,6 +119,7 @@ u64 stable_page_flags(struct page *page)
 	if (!page)
 		return 1 << KPF_NOPAGE;
 
+	head = compound_head(page);
 	k = page->flags;
 	u = 0;
 
@@ -127,7 +129,7 @@ u64 stable_page_flags(struct page *page)
 	 * Note that page->_mapcount is overloaded in SLOB/SLUB/SLQB, so the
 	 * simple test in page_mapped() is not enough.
 	 */
-	if (!PageSlab(compound_head(page)) && page_mapped(page))
+	if (!PageSlab(head) && page_mapped(page))
 		u |= 1 << KPF_MMAP;
 	if (PageAnon(page))
 		u |= 1 << KPF_ANON;
@@ -151,8 +153,6 @@ u64 stable_page_flags(struct page *page)
 	 * to make sure a given page is a thp, not a non-huge compound page.
 	 */
 	else if (PageTransCompound(page)) {
-		struct page *head = compound_head(page);
-
 		/* XXX: misses isolated file THPs */
 		if (PageLRU(head) || PageAnon(head))
 			u |= 1 << KPF_THP;
@@ -185,7 +185,7 @@ u64 stable_page_flags(struct page *page)
 	u |= kpf_copy_bit(k, KPF_LOCKED,	PG_locked);
 
 	u |= kpf_copy_bit(k, KPF_SLAB,		PG_slab);
-	if (PageTail(page) && PageSlab(compound_head(page)))
+	if (PageTail(page) && PageSlab(head))
 		u |= 1 << KPF_SLAB;
 
 	u |= kpf_copy_bit(k, KPF_ERROR,		PG_error);
-- 
2.32.0