mm/ksm: add sysfs knobs for advisor

This adds four new knobs for the KSM advisor to influence its behaviour.

The knobs are:
- advisor_mode:
    none:      no advisor (default)
    scan-time: scan time advisor
- advisor_max_cpu: 70 (default, cpu usage percent)
- advisor_min_pages_to_scan: 500 (default)
- advisor_max_pages_to_scan: 30000 (default)
- advisor_target_scan_time: 200 (default in seconds)

The new values will take effect on the next scan round.

Link: https://lkml.kernel.org/r/20231218231054.1625219-3-shr@devkernel.io
Signed-off-by: Stefan Roesch <shr@devkernel.io>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Rik van Riel <riel@surriel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/ksm.c b/mm/ksm.c
index 599f7d209c68d18ab4af5b5f1bf32df4ce91bd57..ce30017455621b4d78835a84df27491ed1e26ffc 100644 (file)
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -338,6 +338,25 @@ enum ksm_advisor_type {
 };
 static enum ksm_advisor_type ksm_advisor;
 
+#ifdef CONFIG_SYSFS
+/*
+ * Only called through the sysfs control interface:
+ */
+
+/* At least scan this many pages per batch. */
+static unsigned long ksm_advisor_min_pages_to_scan = 500;
+
+static void set_advisor_defaults(void)
+{
+       if (ksm_advisor == KSM_ADVISOR_NONE) {
+               ksm_thread_pages_to_scan = DEFAULT_PAGES_TO_SCAN;
+       } else if (ksm_advisor == KSM_ADVISOR_SCAN_TIME) {
+               advisor_ctx = (const struct advisor_ctx){ 0 };
+               ksm_thread_pages_to_scan = ksm_advisor_min_pages_to_scan;
+       }
+}
+#endif /* CONFIG_SYSFS */
+
 static inline void advisor_start_scan(void)
 {
        if (ksm_advisor == KSM_ADVISOR_SCAN_TIME)
@@ -3721,6 +3740,130 @@ static ssize_t smart_scan_store(struct kobject *kobj,
 }
 KSM_ATTR(smart_scan);
 
+static ssize_t advisor_mode_show(struct kobject *kobj,
+                                struct kobj_attribute *attr, char *buf)
+{
+       const char *output;
+
+       if (ksm_advisor == KSM_ADVISOR_NONE)
+               output = "[none] scan-time";
+       else if (ksm_advisor == KSM_ADVISOR_SCAN_TIME)
+               output = "none [scan-time]";
+
+       return sysfs_emit(buf, "%s\n", output);
+}
+
+static ssize_t advisor_mode_store(struct kobject *kobj,
+                                 struct kobj_attribute *attr, const char *buf,
+                                 size_t count)
+{
+       enum ksm_advisor_type curr_advisor = ksm_advisor;
+
+       if (sysfs_streq("scan-time", buf))
+               ksm_advisor = KSM_ADVISOR_SCAN_TIME;
+       else if (sysfs_streq("none", buf))
+               ksm_advisor = KSM_ADVISOR_NONE;
+       else
+               return -EINVAL;
+
+       /* Set advisor default values */
+       if (curr_advisor != ksm_advisor)
+               set_advisor_defaults();
+
+       return count;
+}
+KSM_ATTR(advisor_mode);
+
+static ssize_t advisor_max_cpu_show(struct kobject *kobj,
+                                   struct kobj_attribute *attr, char *buf)
+{
+       return sysfs_emit(buf, "%u\n", ksm_advisor_max_cpu);
+}
+
+static ssize_t advisor_max_cpu_store(struct kobject *kobj,
+                                    struct kobj_attribute *attr,
+                                    const char *buf, size_t count)
+{
+       int err;
+       unsigned long value;
+
+       err = kstrtoul(buf, 10, &value);
+       if (err)
+               return -EINVAL;
+
+       ksm_advisor_max_cpu = value;
+       return count;
+}
+KSM_ATTR(advisor_max_cpu);
+
+static ssize_t advisor_min_pages_to_scan_show(struct kobject *kobj,
+                                       struct kobj_attribute *attr, char *buf)
+{
+       return sysfs_emit(buf, "%lu\n", ksm_advisor_min_pages_to_scan);
+}
+
+static ssize_t advisor_min_pages_to_scan_store(struct kobject *kobj,
+                                       struct kobj_attribute *attr,
+                                       const char *buf, size_t count)
+{
+       int err;
+       unsigned long value;
+
+       err = kstrtoul(buf, 10, &value);
+       if (err)
+               return -EINVAL;
+
+       ksm_advisor_min_pages_to_scan = value;
+       return count;
+}
+KSM_ATTR(advisor_min_pages_to_scan);
+
+static ssize_t advisor_max_pages_to_scan_show(struct kobject *kobj,
+                                       struct kobj_attribute *attr, char *buf)
+{
+       return sysfs_emit(buf, "%lu\n", ksm_advisor_max_pages_to_scan);
+}
+
+static ssize_t advisor_max_pages_to_scan_store(struct kobject *kobj,
+                                       struct kobj_attribute *attr,
+                                       const char *buf, size_t count)
+{
+       int err;
+       unsigned long value;
+
+       err = kstrtoul(buf, 10, &value);
+       if (err)
+               return -EINVAL;
+
+       ksm_advisor_max_pages_to_scan = value;
+       return count;
+}
+KSM_ATTR(advisor_max_pages_to_scan);
+
+static ssize_t advisor_target_scan_time_show(struct kobject *kobj,
+                                            struct kobj_attribute *attr, char *buf)
+{
+       return sysfs_emit(buf, "%lu\n", ksm_advisor_target_scan_time);
+}
+
+static ssize_t advisor_target_scan_time_store(struct kobject *kobj,
+                                             struct kobj_attribute *attr,
+                                             const char *buf, size_t count)
+{
+       int err;
+       unsigned long value;
+
+       err = kstrtoul(buf, 10, &value);
+       if (err)
+               return -EINVAL;
+       if (value < 1)
+               return -EINVAL;
+
+       ksm_advisor_target_scan_time = value;
+       return count;
+}
+KSM_ATTR(advisor_target_scan_time);
+
 static struct attribute *ksm_attrs[] = {
        &sleep_millisecs_attr.attr,
        &pages_to_scan_attr.attr,
@@ -3743,6 +3886,11 @@ static struct attribute *ksm_attrs[] = {
        &use_zero_pages_attr.attr,
        &general_profit_attr.attr,
        &smart_scan_attr.attr,
+       &advisor_mode_attr.attr,
+       &advisor_max_cpu_attr.attr,
+       &advisor_min_pages_to_scan_attr.attr,
+       &advisor_max_pages_to_scan_attr.attr,
+       &advisor_target_scan_time_attr.attr,
        NULL,
 };