[RFC PATCH 2/3] mm, thp: convert from optimistic to conservative
From: Ebru Akagunduz
Date: Sat Jun 11 2016 - 15:16:25 EST
Currently, khugepaged collapses pages saying only
a referenced page enough to create a THP.
This patch changes the design from optimistic to conservative.
It gives a default threshold which is half of HPAGE_PMD_NR
for referenced pages, also introduces a new sysfs knob.
Signed-off-by: Ebru Akagunduz <ebru.akagunduz@xxxxxxxxx>
---
include/trace/events/huge_memory.h | 10 ++++----
mm/khugepaged.c | 50 +++++++++++++++++++++++++++++---------
2 files changed, 44 insertions(+), 16 deletions(-)
diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h
index 830d47d..5f14025 100644
--- a/include/trace/events/huge_memory.h
+++ b/include/trace/events/huge_memory.h
@@ -13,7 +13,7 @@
EM( SCAN_EXCEED_NONE_PTE, "exceed_none_pte") \
EM( SCAN_PTE_NON_PRESENT, "pte_non_present") \
EM( SCAN_PAGE_RO, "no_writable_page") \
- EM( SCAN_NO_REFERENCED_PAGE, "no_referenced_page") \
+ EM( SCAN_LACK_REFERENCED_PAGE, "lack_referenced_page") \
EM( SCAN_PAGE_NULL, "page_null") \
EM( SCAN_SCAN_ABORT, "scan_aborted") \
EM( SCAN_PAGE_COUNT, "not_suitable_page_count") \
@@ -47,7 +47,7 @@ SCAN_STATUS
TRACE_EVENT(mm_khugepaged_scan_pmd,
TP_PROTO(struct mm_struct *mm, struct page *page, bool writable,
- bool referenced, int none_or_zero, int status, int unmapped),
+ int referenced, int none_or_zero, int status, int unmapped),
TP_ARGS(mm, page, writable, referenced, none_or_zero, status, unmapped),
@@ -55,7 +55,7 @@ TRACE_EVENT(mm_khugepaged_scan_pmd,
__field(struct mm_struct *, mm)
__field(unsigned long, pfn)
__field(bool, writable)
- __field(bool, referenced)
+ __field(int, referenced)
__field(int, none_or_zero)
__field(int, status)
__field(int, unmapped)
@@ -108,14 +108,14 @@ TRACE_EVENT(mm_collapse_huge_page,
TRACE_EVENT(mm_collapse_huge_page_isolate,
TP_PROTO(struct page *page, int none_or_zero,
- bool referenced, bool writable, int status),
+ int referenced, bool writable, int status),
TP_ARGS(page, none_or_zero, referenced, writable, status),
TP_STRUCT__entry(
__field(unsigned long, pfn)
__field(int, none_or_zero)
- __field(bool, referenced)
+ __field(int, referenced)
__field(bool, writable)
__field(int, status)
),
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index e3d8da7..43fc41e 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -27,7 +27,7 @@ enum scan_result {
SCAN_EXCEED_NONE_PTE,
SCAN_PTE_NON_PRESENT,
SCAN_PAGE_RO,
- SCAN_NO_REFERENCED_PAGE,
+ SCAN_LACK_REFERENCED_PAGE,
SCAN_PAGE_NULL,
SCAN_SCAN_ABORT,
SCAN_PAGE_COUNT,
@@ -68,6 +68,7 @@ static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
*/
static unsigned int khugepaged_max_ptes_none __read_mostly;
static unsigned int khugepaged_max_ptes_swap __read_mostly;
+static unsigned int khugepaged_min_ptes_young __read_mostly;
static int khugepaged(void *none);
@@ -282,6 +283,32 @@ static struct kobj_attribute khugepaged_max_ptes_swap_attr =
__ATTR(max_ptes_swap, 0644, khugepaged_max_ptes_swap_show,
khugepaged_max_ptes_swap_store);
+static ssize_t khugepaged_min_ptes_young_show(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ char *buf)
+{
+ return sprintf(buf, "%u\n", khugepaged_min_ptes_young);
+}
+
+static ssize_t khugepaged_min_ptes_young_store(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ const char *buf, size_t count)
+{
+ int err;
+ unsigned long min_ptes_young;
+ err = kstrtoul(buf, 10, &min_ptes_young);
+ if (err || min_ptes_young > HPAGE_PMD_NR-1)
+ return -EINVAL;
+
+ khugepaged_min_ptes_young = min_ptes_young;
+
+ return count;
+}
+
+static struct kobj_attribute khugepaged_min_ptes_young_attr =
+ __ATTR(min_ptes_young, 0644, khugepaged_min_ptes_young_show,
+ khugepaged_min_ptes_young_store);
+
static struct attribute *khugepaged_attr[] = {
&khugepaged_defrag_attr.attr,
&khugepaged_max_ptes_none_attr.attr,
@@ -291,6 +318,7 @@ static struct attribute *khugepaged_attr[] = {
&scan_sleep_millisecs_attr.attr,
&alloc_sleep_millisecs_attr.attr,
&khugepaged_max_ptes_swap_attr.attr,
+ &khugepaged_min_ptes_young_attr.attr,
NULL,
};
@@ -502,8 +530,8 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
{
struct page *page = NULL;
pte_t *_pte;
- int none_or_zero = 0, result = 0;
- bool referenced = false, writable = false;
+ int none_or_zero = 0, result = 0, referenced = 0;
+ bool writable = false;
for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
_pte++, address += PAGE_SIZE) {
@@ -582,14 +610,14 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
VM_BUG_ON_PAGE(!PageLocked(page), page);
VM_BUG_ON_PAGE(PageLRU(page), page);
- /* If there is no mapped pte young don't collapse the page */
+ /* There should be enough young pte to collapse the page */
if (pte_young(pteval) ||
page_is_young(page) || PageReferenced(page) ||
mmu_notifier_test_young(vma->vm_mm, address))
- referenced = true;
+ referenced++;
}
if (likely(writable)) {
- if (likely(referenced)) {
+ if (referenced >= khugepaged_min_ptes_young) {
result = SCAN_SUCCEED;
trace_mm_collapse_huge_page_isolate(page, none_or_zero,
referenced, writable, result);
@@ -1082,11 +1110,11 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
pmd_t *pmd;
pte_t *pte, *_pte;
int ret = 0, none_or_zero = 0, result = 0;
+ int node = NUMA_NO_NODE, unmapped = 0, referenced = 0;
struct page *page = NULL;
unsigned long _address;
spinlock_t *ptl;
- int node = NUMA_NO_NODE, unmapped = 0;
- bool writable = false, referenced = false;
+ bool writable = false;
VM_BUG_ON(address & ~HPAGE_PMD_MASK);
@@ -1174,14 +1202,14 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
if (pte_young(pteval) ||
page_is_young(page) || PageReferenced(page) ||
mmu_notifier_test_young(vma->vm_mm, address))
- referenced = true;
+ referenced++;
}
if (writable) {
- if (referenced) {
+ if (referenced >= khugepaged_min_ptes_young) {
result = SCAN_SUCCEED;
ret = 1;
} else {
- result = SCAN_NO_REFERENCED_PAGE;
+ result = SCAN_LACK_REFERENCED_PAGE;
}
} else {
result = SCAN_PAGE_RO;
--
1.9.1