[RFC v2 2/3] mm: make optimistic check for swapin readahead

Ebru Akagunduz
2015-06-20T11:28:57Z

This patch makes optimistic check for swapin readahead
to increase thp collapse rate. Before getting swapped
out pages to memory, checks them and allows up to a
certain number. It also prints out using tracepoints
amount of unmapped ptes.

Signed-off-by: Ebru Akagunduz <ebru.akagunduz@gmail.com>
---
Changes in v2:
- Nothing changed

include/trace/events/huge_memory.h | 11 +++++++----
mm/huge_memory.c | 13 ++++++++++---
2 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h
index 4b9049b..53c9f2e 100644
--- a/include/trace/events/huge_memory.h
+++ b/include/trace/events/huge_memory.h
@@ -9,9 +9,9 @@
TRACE_EVENT(mm_khugepaged_scan_pmd,

TP_PROTO(struct mm_struct *mm, unsigned long vm_start, bool writable,
- bool referenced, int none_or_zero, int collapse),
+ bool referenced, int none_or_zero, int collapse, int unmapped),

- TP_ARGS(mm, vm_start, writable, referenced, none_or_zero, collapse),
+ TP_ARGS(mm, vm_start, writable, referenced, none_or_zero, collapse, unmapped),

TP_STRUCT__entry(
__field(struct mm_struct *, mm)
@@ -20,6 +20,7 @@ TRACE_EVENT(mm_khugepaged_scan_pmd,
__field(bool, referenced)
__field(int, none_or_zero)
__field(int, collapse)
+ __field(int, unmapped)
),

TP_fast_assign(
@@ -29,15 +30,17 @@ TRACE_EVENT(mm_khugepaged_scan_pmd,
__entry->referenced = referenced;
__entry->none_or_zero = none_or_zero;
__entry->collapse = collapse;
+ __entry->unmapped = unmapped;
),

- TP_printk("mm=%p, vm_start=%04lx, writable=%d, referenced=%d, none_or_zero=%d, collapse=%d",
+ TP_printk("mm=%p, vm_start=%04lx, writable=%d, referenced=%d, none_or_zero=%d, collapse=%d, unmapped=%d",
__entry->mm,
__entry->vm_start,
__entry->writable,
__entry->referenced,
__entry->none_or_zero,
- __entry->collapse)
+ __entry->collapse,
+ __entry->unmapped)
);

TRACE_EVENT(mm_collapse_huge_page,
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 9bb97fc..22bc0bf 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -24,6 +24,7 @@
#include <linux/migrate.h>
#include <linux/hashtable.h>
#include <linux/userfaultfd_k.h>
+#include <linux/swapops.h>

#include <asm/tlb.h>
#include <asm/pgalloc.h>
@@ -2639,11 +2640,11 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
{
pmd_t *pmd;
pte_t *pte, *_pte;
- int ret = 0, none_or_zero = 0;
+ int ret = 0, none_or_zero = 0, unmapped = 0;
struct page *page;
unsigned long _address;
spinlock_t *ptl;
- int node = NUMA_NO_NODE;
+ int node = NUMA_NO_NODE, max_ptes_swap = HPAGE_PMD_NR/8;
bool writable = false, referenced = false;

VM_BUG_ON(address & ~HPAGE_PMD_MASK);
@@ -2657,6 +2658,12 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR;
_pte++, _address += PAGE_SIZE) {
pte_t pteval = *_pte;
+ if (is_swap_pte(pteval)) {
+ if (++unmapped <= max_ptes_swap)
+ continue;
+ else
+ goto out_unmap;
+ }
if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
if (!userfaultfd_armed(vma) &&
++none_or_zero <= khugepaged_max_ptes_none)
@@ -2701,7 +2708,7 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
out_unmap:
pte_unmap_unlock(pte, ptl);
trace_mm_khugepaged_scan_pmd(mm, vma->vm_start, writable, referenced,
- none_or_zero, ret);
+ none_or_zero, ret, unmapped);
if (ret) {
node = khugepaged_find_target_node();
/* collapse_huge_page will return with the mmap_sem released */
--
1.9.1