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From:   Stefan Roesch <shr@devkernel.io>
To:     kernel-team@fb.com
Cc:     shr@devkernel.io, akpm@linux-foundation.org, david@redhat.com,
        hannes@cmpxchg.org, riel@surriel.com, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: [PATCH v4 2/4] mm/ksm: add pages_skipped metric
Date:   Wed, 27 Sep 2023 09:22:20 -0700
Message-Id: <20230927162222.3827551-3-shr@devkernel.io>
In-Reply-To: <20230927162222.3827551-1-shr@devkernel.io>
References: <20230927162222.3827551-1-shr@devkernel.io>
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This change adds the "pages skipped" metric. To be able to evaluate how
successful smart page scanning is, the pages skipped metric can be
compared to the pages scanned metric.

The pages skipped metric is a cumulative counter. The counter is stored
under /sys/kernel/mm/ksm/pages_skipped.

Signed-off-by: Stefan Roesch <shr@devkernel.io>
Reviewed-by: David Hildenbrand <david@redhat.com>
---
 mm/ksm.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/mm/ksm.c b/mm/ksm.c
index c0a2e7759365..1df25a66f162 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -293,6 +293,9 @@ static bool ksm_smart_scan =3D 1;
 /* The number of zero pages which is placed by KSM */
 unsigned long ksm_zero_pages;
=20
+/* The number of pages that have been skipped due to "smart scanning" */
+static unsigned long ksm_pages_skipped;
+
 #ifdef CONFIG_NUMA
 /* Zeroed when merging across nodes is not allowed */
 static unsigned int ksm_merge_across_nodes =3D 1;
@@ -2376,6 +2379,7 @@ static bool should_skip_rmap_item(struct page *page=
,
 	}
=20
 	/* Skip this page */
+	ksm_pages_skipped++;
 	rmap_item->remaining_skips--;
 	remove_rmap_item_from_tree(rmap_item);
 	return true;
@@ -3463,6 +3467,13 @@ static ssize_t pages_volatile_show(struct kobject =
*kobj,
 }
 KSM_ATTR_RO(pages_volatile);
=20
+static ssize_t pages_skipped_show(struct kobject *kobj,
+				  struct kobj_attribute *attr, char *buf)
+{
+	return sysfs_emit(buf, "%lu\n", ksm_pages_skipped);
+}
+KSM_ATTR_RO(pages_skipped);
+
 static ssize_t ksm_zero_pages_show(struct kobject *kobj,
 				struct kobj_attribute *attr, char *buf)
 {
@@ -3560,6 +3571,7 @@ static struct attribute *ksm_attrs[] =3D {
 	&pages_sharing_attr.attr,
 	&pages_unshared_attr.attr,
 	&pages_volatile_attr.attr,
+	&pages_skipped_attr.attr,
 	&ksm_zero_pages_attr.attr,
 	&full_scans_attr.attr,
 #ifdef CONFIG_NUMA
--=20
2.39.3