Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Message-Id: <7126e8b14b566b756d1fbfa31f09898b35fd8bba.1539931702.git.christophe.leroy@c-s.fr>
In-Reply-To: <cover.1539931702.git.christophe.leroy@c-s.fr>
References: <cover.1539931702.git.christophe.leroy@c-s.fr>
From:   Christophe Leroy <christophe.leroy@c-s.fr>
Subject: [PATCH v6 03/20] powerpc/mm: Avoid useless lock with single page
 fragments
To:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Date:   Fri, 19 Oct 2018 06:54:58 +0000 (UTC)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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@linux.ibm.com>
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.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 84ff3403239c..9f78db7c8c2a 100644
--- a/arch/powerpc/mm/pgtable-book3s64.c
+++ b/arch/powerpc/mm/pgtable-book3s64.c
@@ -243,6 +243,9 @@ 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