linux-kernel - [PATCH v4 15/20] powerpc/mm: Avoid useless lock with single page fragments

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Message-Id: <7efec0c76fa692513c806871151a7ae20e99fe05.1537288312.git.christophe.leroy@c-s.fr>
Date:   Tue, 18 Sep 2018 16:57:32 +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>,
        aneesh.kumar@...ux.vnet.ibm.com
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH v4 15/20] powerpc/mm: Avoid useless lock with single page
 fragments

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

Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
---
 arch/powerpc/mm/pgtable-frag.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/powerpc/mm/pgtable-frag.c b/arch/powerpc/mm/pgtable-frag.c
index bc924822dcd6..ab4910e92aaf 100644
--- a/arch/powerpc/mm/pgtable-frag.c
+++ b/arch/powerpc/mm/pgtable-frag.c
@@ -85,6 +85,9 @@ 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