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Subject[RESEND RFC v4 2/3] mm: make optimistic check for swapin readahead
Date
This patch introduces new sysfs integer knob
/sys/kernel/mm/transparent_hugepage/khugepaged/max_ptes_swap
which 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

Changes in v3:
- Define constant for exact tracepoint result (Vlastimil Babka)

Changes in v4:
- Add sysfs knob request (Kirill A. Shutemov)

include/trace/events/huge_memory.h | 10 ++++----
mm/huge_memory.c | 48 ++++++++++++++++++++++++++++++++++----
2 files changed, 50 insertions(+), 8 deletions(-)

diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h
index 36162a9..c2112fd 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 pfn, bool writable,
- bool referenced, int none_or_zero, int status),
+ bool referenced, int none_or_zero, int status, int unmapped),

- TP_ARGS(mm, pfn, writable, referenced, none_or_zero, status),
+ TP_ARGS(mm, pfn, writable, referenced, none_or_zero, status, 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, status)
+ __field(int, unmapped)
),

TP_fast_assign(
@@ -31,13 +32,14 @@ TRACE_EVENT(mm_khugepaged_scan_pmd,
__entry->status = status;
),

- TP_printk("mm=%p, scan_pfn=0x%lx, writable=%d, referenced=%d, none_or_zero=%d, status=%s",
+ TP_printk("mm=%p, scan_pfn=0x%lx, writable=%d, referenced=%d, none_or_zero=%d, status=%s, unmapped=%d",
__entry->mm,
__entry->pfn,
__entry->writable,
__entry->referenced,
__entry->none_or_zero,
- khugepaged_status_string[__entry->status])
+ khugepaged_status_string[__entry->status],
+ __entry->unmapped)
);

TRACE_EVENT(mm_collapse_huge_page,
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 71a7c43..cb9ab46 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -23,6 +23,7 @@
#include <linux/pagemap.h>
#include <linux/migrate.h>
#include <linux/hashtable.h>
+#include <linux/swapops.h>

#include <asm/tlb.h>
#include <asm/pgalloc.h>
@@ -49,7 +50,8 @@ static const char *const khugepaged_status_string[] = {
"page_swap_cache",
"could_not_delete_page_from_lru",
"alloc_huge_page_fail",
- "ccgroup_charge_fail"
+ "ccgroup_charge_fail",
+ "exceed_swap_pte"
};

enum scan_result {
@@ -73,7 +75,8 @@ enum scan_result {
SCAN_SWAP_CACHE_PAGE,
SCAN_DEL_PAGE_LRU,
SCAN_ALLOC_HUGE_PAGE_FAIL,
- SCAN_CGROUP_CHARGE_FAIL
+ SCAN_CGROUP_CHARGE_FAIL,
+ MM_EXCEED_SWAP_PTE
};

#define CREATE_TRACE_POINTS
@@ -115,6 +118,7 @@ static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
* fault.
*/
static unsigned int khugepaged_max_ptes_none __read_mostly = HPAGE_PMD_NR-1;
+static unsigned int khugepaged_max_ptes_swap __read_mostly = HPAGE_PMD_NR/8;

static int khugepaged(void *none);
static int khugepaged_slab_init(void);
@@ -607,6 +611,33 @@ static struct kobj_attribute khugepaged_max_ptes_none_attr =
__ATTR(max_ptes_none, 0644, khugepaged_max_ptes_none_show,
khugepaged_max_ptes_none_store);

+static ssize_t khugepaged_max_ptes_swap_show(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ char *buf)
+{
+ return sprintf(buf, "%u\n", khugepaged_max_ptes_swap);
+}
+
+static ssize_t khugepaged_max_ptes_swap_store(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ const char *buf, size_t count)
+{
+ int err;
+ unsigned long max_ptes_swap;
+
+ err = kstrtoul(buf, 10, &max_ptes_swap);
+ if (err || max_ptes_swap > HPAGE_PMD_NR-1)
+ return -EINVAL;
+
+ khugepaged_max_ptes_swap = max_ptes_swap;
+
+ return count;
+}
+
+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 struct attribute *khugepaged_attr[] = {
&khugepaged_defrag_attr.attr,
&khugepaged_max_ptes_none_attr.attr,
@@ -615,6 +646,7 @@ static struct attribute *khugepaged_attr[] = {
&full_scans_attr.attr,
&scan_sleep_millisecs_attr.attr,
&alloc_sleep_millisecs_attr.attr,
+ &khugepaged_max_ptes_swap_attr.attr,
NULL,
};

@@ -2664,7 +2696,7 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
struct page *page = NULL;
unsigned long _address;
spinlock_t *ptl;
- int node = NUMA_NO_NODE;
+ int node = NUMA_NO_NODE, unmapped = 0;
bool writable = false, referenced = false;

VM_BUG_ON(address & ~HPAGE_PMD_MASK);
@@ -2680,6 +2712,14 @@ 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 <= khugepaged_max_ptes_swap) {
+ continue;
+ } else {
+ result = MM_EXCEED_SWAP_PTE;
+ goto out_unmap;
+ }
+ }
if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
if (++none_or_zero <= khugepaged_max_ptes_none) {
continue;
@@ -2757,7 +2797,7 @@ out_unmap:
}
out:
trace_mm_khugepaged_scan_pmd(mm, page_to_pfn(page), writable, referenced,
- none_or_zero, result);
+ none_or_zero, result, unmapped);
return ret;
}

--
1.9.1


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