linux-kernel - [PATCH v7 04/16] powerpc/mm: Avoid useless lock with single page fragments

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Message-Id: <3b06c670786936f1fa184dffb815824b10c6e761.1543405086.git.christophe.leroy@c-s.fr>
Date:   Wed, 28 Nov 2018 11:46:29 +0000 (UTC)
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH v7 04/16] powerpc/mm: Avoid useless lock with single page
 fragments

There is no point in taking the page table lock as pte_frag or
pmd_frag are always NULL when we have only one fragment.

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
---
 arch/powerpc/mm/pgtable-book3s64.c | 3 +++
 arch/powerpc/mm/pgtable-frag.c     | 3 +++
 2 files changed, 6 insertions(+)

diff --git a/arch/powerpc/mm/pgtable-book3s64.c b/arch/powerpc/mm/pgtable-book3s64.c
index 0c0fd173208a..f3c31f5e1026 100644
--- a/arch/powerpc/mm/pgtable-book3s64.c
+++ b/arch/powerpc/mm/pgtable-book3s64.c
@@ -244,6 +244,9 @@ static pmd_t *get_pmd_from_cache(struct mm_struct *mm)
 {
 	void *pmd_frag, *ret;
 
+	if (PMD_FRAG_NR == 1)
+		return NULL;
+
 	spin_lock(&mm->page_table_lock);
 	ret = mm->context.pmd_frag;
 	if (ret) {
diff --git a/arch/powerpc/mm/pgtable-frag.c b/arch/powerpc/mm/pgtable-frag.c
index d61e7c2a9a79..7544d0d7177d 100644
--- a/arch/powerpc/mm/pgtable-frag.c
+++ b/arch/powerpc/mm/pgtable-frag.c
@@ -34,6 +34,9 @@ static pte_t *get_pte_from_cache(struct mm_struct *mm)
 {
 	void *pte_frag, *ret;
 
+	if (PTE_FRAG_NR == 1)
+		return NULL;
+
 	spin_lock(&mm->page_table_lock);
 	ret = mm->context.pte_frag;
 	if (ret) {
-- 
2.13.3