Add .is_khugepaged flag to struct collapse_control so
khugepaged-specific behavior can be elided by MADV_COLLAPSE context.
Start by protecting khugepaged-specific heuristics by this flag. In
MADV_COLLAPSE, the user presumably has reason to believe the collapse
will be beneficial and khugepaged heuristics shouldn't prevent the user
from doing so:
1) sysfs-controlled knobs khugepaged_max_ptes_[none|swap|shared]
2) requirement that some pages in region being collapsed be young or
referenced
Signed-off-by: Zach O'Keefe <zokeefe@xxxxxxxxxx>
---
v6 -> v7: There is no functional change here from v6, just a renaming of
flags to explicitly be predicated on khugepaged.
---
mm/khugepaged.c | 62 ++++++++++++++++++++++++++++++++++---------------
1 file changed, 43 insertions(+), 19 deletions(-)
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 147f5828f052..d89056d8cbad 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -73,6 +73,8 @@ static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
* default collapse hugepages if there is at least one pte mapped like
* it would have happened if the vma was large enough during page
* fault.
+ *
+ * Note that these are only respected if collapse was initiated by khugepaged.
*/
static unsigned int khugepaged_max_ptes_none __read_mostly;
static unsigned int khugepaged_max_ptes_swap __read_mostly;
@@ -86,6 +88,8 @@ static struct kmem_cache *mm_slot_cache __read_mostly;
#define MAX_PTE_MAPPED_THP 8
struct collapse_control {
+ bool is_khugepaged;
+
/* Num pages scanned per node */
int node_load[MAX_NUMNODES];
@@ -554,6 +558,7 @@ static bool is_refcount_suitable(struct page *page)
static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
unsigned long address,
pte_t *pte,
+ struct collapse_control *cc,
struct list_head *compound_pagelist)
{
struct page *page = NULL;
@@ -567,7 +572,8 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
if (pte_none(pteval) || (pte_present(pteval) &&
is_zero_pfn(pte_pfn(pteval)))) {
if (!userfaultfd_armed(vma) &&
- ++none_or_zero <= khugepaged_max_ptes_none) {
+ (++none_or_zero <= khugepaged_max_ptes_none ||
+ !cc->is_khugepaged)) {
continue;
} else {
result = SCAN_EXCEED_NONE_PTE;
@@ -587,8 +593,8 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
VM_BUG_ON_PAGE(!PageAnon(page), page);
- if (page_mapcount(page) > 1 &&
- ++shared > khugepaged_max_ptes_shared) {
+ if (cc->is_khugepaged && page_mapcount(page) > 1 &&
+ ++shared > khugepaged_max_ptes_shared) {
result = SCAN_EXCEED_SHARED_PTE;
count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
goto out;
@@ -654,10 +660,14 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
if (PageCompound(page))
list_add_tail(&page->lru, compound_pagelist);
next:
- /* 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))
+ /*
+ * If collapse was initiated by khugepaged, check that there is
+ * enough young pte to justify collapsing the page
+ */
+ if (cc->is_khugepaged &&
+ (pte_young(pteval) || page_is_young(page) ||
+ PageReferenced(page) || mmu_notifier_test_young(vma->vm_mm,
+ address)))
referenced++;
if (pte_write(pteval))
@@ -666,7 +676,7 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
if (unlikely(!writable)) {
result = SCAN_PAGE_RO;
- } else if (unlikely(!referenced)) {
+ } else if (unlikely(cc->is_khugepaged && !referenced)) {
result = SCAN_LACK_REFERENCED_PAGE;
} else {
result = SCAN_SUCCEED;
@@ -745,6 +755,7 @@ static void khugepaged_alloc_sleep(void)
struct collapse_control khugepaged_collapse_control = {
+ .is_khugepaged = true,
.last_target_node = NUMA_NO_NODE,
};
@@ -1023,7 +1034,7 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address,
mmu_notifier_invalidate_range_end(&range);
spin_lock(pte_ptl);
- result = __collapse_huge_page_isolate(vma, address, pte,
+ result = __collapse_huge_page_isolate(vma, address, pte, cc,
&compound_pagelist);
spin_unlock(pte_ptl);
@@ -1114,7 +1125,8 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
_pte++, _address += PAGE_SIZE) {
pte_t pteval = *_pte;
if (is_swap_pte(pteval)) {
- if (++unmapped <= khugepaged_max_ptes_swap) {
+ if (++unmapped <= khugepaged_max_ptes_swap ||
+ !cc->is_khugepaged) {
/*
* Always be strict with uffd-wp
* enabled swap entries. Please see
@@ -1133,7 +1145,8 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
}
if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
if (!userfaultfd_armed(vma) &&
- ++none_or_zero <= khugepaged_max_ptes_none) {
+ (++none_or_zero <= khugepaged_max_ptes_none ||
+ !cc->is_khugepaged)) {
continue;
} else {
result = SCAN_EXCEED_NONE_PTE;
@@ -1163,8 +1176,9 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
goto out_unmap;
}
- if (page_mapcount(page) > 1 &&
- ++shared > khugepaged_max_ptes_shared) {
+ if (cc->is_khugepaged &&
+ page_mapcount(page) > 1 &&
+ ++shared > khugepaged_max_ptes_shared) {
result = SCAN_EXCEED_SHARED_PTE;
count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
goto out_unmap;
@@ -1218,14 +1232,22 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
result = SCAN_PAGE_COUNT;
goto out_unmap;
}
- if (pte_young(pteval) ||
- page_is_young(page) || PageReferenced(page) ||
- mmu_notifier_test_young(vma->vm_mm, address))
+
+ /*
+ * If collapse was initiated by khugepaged, check that there is
+ * enough young pte to justify collapsing the page
+ */
+ if (cc->is_khugepaged &&
+ (pte_young(pteval) || page_is_young(page) ||
+ PageReferenced(page) || mmu_notifier_test_young(vma->vm_mm,
+ address)))
referenced++;
}
if (!writable) {
result = SCAN_PAGE_RO;
- } else if (!referenced || (unmapped && referenced < HPAGE_PMD_NR/2)) {
+ } else if (cc->is_khugepaged &&
+ (!referenced ||
+ (unmapped && referenced < HPAGE_PMD_NR / 2))) {
result = SCAN_LACK_REFERENCED_PAGE;
} else {
result = SCAN_SUCCEED;
@@ -1894,7 +1916,8 @@ static int khugepaged_scan_file(struct mm_struct *mm, struct file *file,
continue;
if (xa_is_value(page)) {
- if (++swap > khugepaged_max_ptes_swap) {
+ if (cc->is_khugepaged &&
+ ++swap > khugepaged_max_ptes_swap) {
result = SCAN_EXCEED_SWAP_PTE;
count_vm_event(THP_SCAN_EXCEED_SWAP_PTE);
break;
@@ -1945,7 +1968,8 @@ static int khugepaged_scan_file(struct mm_struct *mm, struct file *file,
rcu_read_unlock();
if (result == SCAN_SUCCEED) {
- if (present < HPAGE_PMD_NR - khugepaged_max_ptes_none) {
+ if (present < HPAGE_PMD_NR - khugepaged_max_ptes_none &&
+ cc->is_khugepaged) {
result = SCAN_EXCEED_NONE_PTE;
count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
} else {
--
2.37.0.rc0.161.g10f37bed90-goog
