[PATCH v6 03/20] powerpc/mm: Avoid useless lock with single page fragments

From: Christophe Leroy
Date: Fri Oct 19 2018 - 02:55:02 EST


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@xxxxxxxxxxxxx>
Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
---
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