[PATCH v1] mm/ksm: add pages scanned metric

Stefan Roesch
2023-08-11T19:37:16Z

ksm currently maintains several statistics, which let you determine how
successful KSM is at sharing pages. However it does not contain a metric
to determine how much work it does.

This commit adds the pages scanned metric. This allows the administrator
to determine how many pages have been scanned over a period of time.

Signed-off-by: Stefan Roesch <shr@devkernel.io>
---
Documentation/admin-guide/mm/ksm.rst | 2 ++
mm/ksm.c | 16 +++++++++++++++-
2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/mm/ksm.rst b/Documentation/admin-guide/mm/ksm.rst
index 5c5be7bd84b8..776f244bdae4 100644
--- a/Documentation/admin-guide/mm/ksm.rst
+++ b/Documentation/admin-guide/mm/ksm.rst
@@ -159,6 +159,8 @@ The effectiveness of KSM and MADV_MERGEABLE is shown in ``/sys/kernel/mm/ksm/``:

general_profit
how effective is KSM. The calculation is explained below.
+pages_scanned
+ how many pages are being scanned for ksm
pages_shared
how many shared pages are being used
pages_sharing
diff --git a/mm/ksm.c b/mm/ksm.c
index 6b7b8928fb96..8d6aee05421d 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -242,6 +242,9 @@ static struct kmem_cache *rmap_item_cache;
static struct kmem_cache *stable_node_cache;
static struct kmem_cache *mm_slot_cache;

+/* The number of pages scanned */
+static unsigned long ksm_pages_scanned;
+
/* The number of nodes in the stable tree */
static unsigned long ksm_pages_shared;

@@ -2483,8 +2486,9 @@ static void ksm_do_scan(unsigned int scan_npages)
{
struct ksm_rmap_item *rmap_item;
struct page *page;
+ unsigned int npages = scan_npages;

- while (scan_npages-- && likely(!freezing(current))) {
+ while (npages-- && likely(!freezing(current))) {
cond_resched();
rmap_item = scan_get_next_rmap_item(&page);
if (!rmap_item)
@@ -2492,6 +2496,8 @@ static void ksm_do_scan(unsigned int scan_npages)
cmp_and_merge_page(page, rmap_item);
put_page(page);
}
+
+ ksm_pages_scanned += scan_npages - npages;
}

static int ksmd_should_run(void)
@@ -3332,6 +3338,13 @@ static ssize_t max_page_sharing_store(struct kobject *kobj,
}
KSM_ATTR(max_page_sharing);

+static ssize_t pages_scanned_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ return sysfs_emit(buf, "%lu\n", ksm_pages_scanned);
+}
+KSM_ATTR_RO(pages_scanned);
+
static ssize_t pages_shared_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
@@ -3440,6 +3453,7 @@ static struct attribute *ksm_attrs[] = {
&sleep_millisecs_attr.attr,
&pages_to_scan_attr.attr,
&run_attr.attr,
+ &pages_scanned_attr.attr,
&pages_shared_attr.attr,
&pages_sharing_attr.attr,
&pages_unshared_attr.attr,

base-commit: f4a280e5bb4a764a75d3215b61bc0f02b4c26417
--
2.39.3