[...]
+
+/**
+ * struct advisor_ctx - metadata for KSM advisor
+ * @start_scan: start time of the current scan
+ * @scan_time: scan time of previous scan
+ * @change: change in percent to pages_to_scan parameter
+ * @cpu_time: cpu time consumed by the ksmd thread in the previous scan
+ */
+struct advisor_ctx {
+ ktime_t start_scan;
+ unsigned long scan_time;
+ unsigned long change;
+ unsigned long long cpu_time;
+};
+static struct advisor_ctx advisor_ctx;
+
+/* Define different advisor's */
+enum ksm_advisor_type {
+ KSM_ADVISOR_NONE,
+ KSM_ADVISOR_SCAN_TIME,
+};
+static enum ksm_advisor_type ksm_advisor;
+
+static void init_advisor(void)
+{
+ advisor_ctx = (const struct advisor_ctx){ 0 };
+}
Again, you can drop this completely. The static values are already
initialized to 0.
Or is there any reason to initialize to 0 explicitly?
+
+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)
+ ksm_thread_pages_to_scan = ksm_advisor_min_pages;
+}
That function is unused?
+
+static inline void advisor_start_scan(void)
+{
+ if (ksm_advisor == KSM_ADVISOR_SCAN_TIME)
+ advisor_ctx.start_scan = ktime_get();
+}
+
+static inline s64 advisor_stop_scan(void)
+{
+ return ktime_ms_delta(ktime_get(), advisor_ctx.start_scan);
+}
Just inline that into the caller. Then rename run_advisor() into
advisor_stop_scan(). So in scan_get_next_rmap_item)( you have paired
start+stop hooks.
+
+/*
+ * Use previous scan time if available, otherwise use current scan time as an
+ * approximation for the previous scan time.
+ */
+static inline unsigned long prev_scan_time(struct advisor_ctx *ctx,
+ unsigned long scan_time)
+{
+ return ctx->scan_time ? ctx->scan_time : scan_time;
+}
+
+/* Calculate exponential weighted moving average */
+static unsigned long ewma(unsigned long prev, unsigned long curr)
+{
+ return ((100 - EWMA_WEIGHT) * prev + EWMA_WEIGHT * curr) / 100;
+}
+
+/*
+ * The scan time advisor is based on the current scan rate and the target
+ * scan rate.
+ *
+ * new_pages_to_scan = pages_to_scan * (scan_time / target_scan_time)
+ *
+ * To avoid pertubations it calculates a change factor of previous changes.
s/pertubations/perturbations/
Do you also want to describe how min/max CPU comes into play?
+ * A new change factor is calculated for each iteration and it uses an
+ * exponentially weighted moving average. The new pages_to_scan value is
+ * multiplied with that change factor:
+ *
+ * new_pages_to_scan *= change facor
+ *
+ * In addition the new pages_to_scan value is capped by the max and min
+ * limits.
+ */
With that, LGTM
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
--
Cheers,
David / dhildenb
