[t:4181] #4181 Make memory accounting a little cleaner.

git-svn-id: file:///svn/toku/tokudb@38050 c7de825b-a66e-492c-adef-691d508d4ae1

linux/memory.c

@@ -67,14 +67,20 @@ my_malloc_usable_size(void *p) {
     return p == NULL ? 0 : malloc_usable_size(p);
 }
 
-// max_in_use may be slightly off because use of max_in_use is not thread-safe.
-// It is not worth the overhead to make it completely accurate.
+// Note that max_in_use may be slightly off because use of max_in_use is not thread-safe.
+// It is not worth the overhead to make it completely accurate, but
+// this logic is intended to guarantee that it increases monotonically.
+// Note that status.sum_used and status.sum_freed increase monotonically
+// and that status.max_in_use is declared volatile.
 static inline void 
 set_max(uint64_t sum_used, uint64_t sum_freed) {
-    uint64_t in_use = (sum_used - sum_freed);
-    if ((!(in_use & 0x8000000000000000)) // if wrap due to another thread, ignore bogus "negative" value
-	&& (in_use > status.max_in_use)) {
-	status.max_in_use = in_use;
+    if (sum_used >= sum_freed) {
+	uint64_t in_use = sum_used - sum_freed;
+	uint64_t old_max;
+	do {
+	    old_max = status.max_in_use;
+	} while (old_max < in_use &&
+		 !__sync_bool_compare_and_swap(&status.max_in_use, old_max, in_use));
     }
 }
 

toku_include/memory.h

@@ -106,7 +106,7 @@ typedef struct memory_status {
     uint64_t requested;       // number of bytes requested
     uint64_t used;            // number of bytes used (requested + overhead), obtained from malloc_usable_size()
     uint64_t freed;           // number of bytes freed;
-    uint64_t max_in_use;      // maximum memory footprint (used - freed), approximate (not worth threadsafety overhead for exact)
+    volatile uint64_t max_in_use;      // maximum memory footprint (used - freed), approximate (not worth threadsafety overhead for exact)
     const char *mallocator_version;
     uint64_t mmap_threshold;
 } MEMORY_STATUS_S, *MEMORY_STATUS;