Add peak_t, for tracking allocator net max.

include/jemalloc/internal/peak.h

@@ -0,0 +1,37 @@
+#ifndef JEMALLOC_INTERNAL_PEAK_H
+#define JEMALLOC_INTERNAL_PEAK_H
+
+typedef struct peak_s peak_t;
+struct peak_s {
+	/* The highest recorded peak value, after adjustment (see below). */
+	uint64_t cur_max;
+	/*
+	 * The difference between alloc and dalloc at the last set_zero call;
+	 * this lets us cancel out the appropriate amount of excess.
+	 */
+	uint64_t adjustment;
+};
+
+#define PEAK_INITIALIZER {0, 0}
+
+static inline uint64_t
+peak_max(peak_t *peak) {
+	return peak->cur_max;
+}
+
+static inline void
+peak_update(peak_t *peak, uint64_t alloc, uint64_t dalloc) {
+	int64_t candidate_max = (int64_t)(alloc - dalloc - peak->adjustment);
+	if (candidate_max > (int64_t)peak->cur_max) {
+		peak->cur_max = candidate_max;
+	}
+}
+
+/* Resets the counter to zero; all peaks are now relative to this point. */
+static inline void
+peak_set_zero(peak_t *peak, uint64_t alloc, uint64_t dalloc) {
+	peak->cur_max = 0;
+	peak->adjustment = alloc - dalloc;
+}
+
+#endif /* JEMALLOC_INTERNAL_PEAK_H */