Kirill A. Shutemov with 8c6e50b029 commit introduced
vm_ops->map_pages() for mapping easy accessible pages around
fault address in hope to reduce number of minor page faults.
This patch creates infrastructure to modify the FAULT_AROUND_ORDER
value using mm/Kconfig. This will enable architecture maintainers
to decide on suitable FAULT_AROUND_ORDER value based on
performance data for that architecture. Patch also defaults
FAULT_AROUND_ORDER Kconfig element to 4.
Signed-off-by: Madhavan Srinivasan <maddy@xxxxxxxxxxxxxxxxxx>
---
mm/Kconfig | 8 ++++++++
mm/memory.c | 25 ++++++-------------------
2 files changed, 14 insertions(+), 19 deletions(-)
diff --git a/mm/Kconfig b/mm/Kconfig
index ebe5880..c7fc4f1 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -176,6 +176,14 @@ config MOVABLE_NODE
config HAVE_BOOTMEM_INFO_NODE
def_bool n
+#
+# Fault around order is a control knob to decide the fault around pages.
+# Default value is set to 4 , but the arch can override it as desired.
+#
+config FAULT_AROUND_ORDER
+ int
+ default 4
+
# eventually, we can have this option just 'select SPARSEMEM'
config MEMORY_HOTPLUG
bool "Allow for memory hot-add"
diff --git a/mm/memory.c b/mm/memory.c
index 037b812..e3931ef 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3402,11 +3402,9 @@ void do_set_pte(struct vm_area_struct *vma, unsigned long address,
update_mmu_cache(vma, address, pte);
}
-#define FAULT_AROUND_ORDER 4
+unsigned int fault_around_order __read_mostly = CONFIG_FAULT_AROUND_ORDER;
#ifdef CONFIG_DEBUG_FS
-static unsigned int fault_around_order = FAULT_AROUND_ORDER;
-
static int fault_around_order_get(void *data, u64 *val)
{
*val = fault_around_order;
@@ -3415,7 +3413,6 @@ static int fault_around_order_get(void *data, u64 *val)
static int fault_around_order_set(void *data, u64 val)
{
- BUILD_BUG_ON((1UL << FAULT_AROUND_ORDER) > PTRS_PER_PTE);
if (1UL << val > PTRS_PER_PTE)
return -EINVAL;
fault_around_order = val;
@@ -3435,31 +3432,21 @@ static int __init fault_around_debugfs(void)
return 0;
}
late_initcall(fault_around_debugfs);
+#endif
static inline unsigned long fault_around_pages(void)
{
- return 1UL << fault_around_order;
-}
-
-static inline unsigned long fault_around_mask(void)
-{
- return ~((1UL << (PAGE_SHIFT + fault_around_order)) - 1);
-}
-#else
-static inline unsigned long fault_around_pages(void)
-{
unsigned long nr_pages;
- nr_pages = 1UL << FAULT_AROUND_ORDER;
- BUILD_BUG_ON(nr_pages > PTRS_PER_PTE);
+ nr_pages = 1UL << fault_around_order;
+ VM_BUG_ON(nr_pages > PTRS_PER_PTE);
return nr_pages;
}
static inline unsigned long fault_around_mask(void)
{
- return ~((1UL << (PAGE_SHIFT + FAULT_AROUND_ORDER)) - 1);
+ return ~((1UL << (PAGE_SHIFT + fault_around_order)) - 1);
}
-#endif
static void do_fault_around(struct vm_area_struct *vma, unsigned long address,
pte_t *pte, pgoff_t pgoff, unsigned int flags)
@@ -3515,7 +3502,7 @@ static int do_read_fault(struct mm_struct *mm, struct vm_area_struct *vma,
* if page by the offset is not ready to be mapped (cold cache or
* something).
*/
- if (vma->vm_ops->map_pages) {
+ if ((vma->vm_ops->map_pages) && fault_around_order) {
pte = pte_offset_map_lock(mm, pmd, address, &ptl);
do_fault_around(vma, address, pte, pgoff, flags);
if (!pte_same(*pte, orig_pte))
--
1.7.10.4
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