[#25436] DocDB: Fix GcMemory result

Summary:
MemTracker::GcMemory tries to release memory, then returns true if we still cannot consume requested amount of bytes.
There is a bug in logic, that return `false` if we already released enough memory.
It could lead to situation when RPC call or response will be rejected due to lack of memory, while actually we could handle it.

Fixed to returning `true` in this case.
Jira: DB-14673

Test Plan: ./yb_build.sh -n 200 --cxx-test redisserver_redisserver-test --gtest_filter TestRedisService.HugeCommandInline

Reviewers: timur

Reviewed By: timur

Subscribers: ybase

Tags: #jenkins-ready

Differential Revision: https://phorge.dev.yugabyte.com/D40911

src/yb/docdb/redis_operation.cc

@@ -1448,8 +1448,9 @@ Status RedisReadOperation::ExecuteHGetAllLikeCommands(ValueEntryType value_type,
 
   RETURN_NOT_OK(GetRedisSubDocument(iterator_.get(), data, /* projection */ nullptr,
                                SeekFwdSuffices::kFalse));
-  if (return_array_response)
+  if (return_array_response) {
     response_.set_allocated_array_response(new RedisArrayPB());
+  }
 
   if (!doc_found) {
     response_.set_code(RedisResponsePB::OK);

src/yb/util/mem_tracker.cc

@@ -518,12 +518,10 @@ bool MemTracker::TryConsume(int64_t bytes, MemTracker** blocking_mem_tracker) {
       if (!TryIncrementBy(bytes, tracker->limit_, &tracker->consumption_, tracker->metrics_)) {
         // One of the trackers failed, attempt to GC memory or expand our limit. If that
         // succeeds, TryUpdate() again. Bail if either fails.
-        if (!tracker->GcMemory(tracker->limit_ - bytes) ||
-            tracker->ExpandLimit(bytes)) {
-          if (!TryIncrementBy(bytes, tracker->limit_, &tracker->consumption_, tracker->metrics_)) {
-            break;
-          }
-        } else {
+        if (tracker->GcMemory(tracker->limit_ - bytes)) {
+          break;
+        }
+        if (!TryIncrementBy(bytes, tracker->limit_, &tracker->consumption_, tracker->metrics_)) {
           break;
         }
       }
@@ -728,7 +726,7 @@ bool MemTracker::GcMemory(int64_t max_consumption) {
       if (did_gc) {
         current_consumption = GetUpdatedConsumption();
         if (current_consumption <= max_consumption) {
-          return true;
+          return false;
         }
       }
     }

src/yb/util/mem_tracker.h

@@ -324,12 +324,6 @@ class MemTracker : public std::enable_shared_from_this<MemTracker> {
   // Increases consumption of this tracker and its ancestors by 'bytes'.
   void Consume(int64_t bytes);
 
-  // Try to expand the limit (by asking the resource broker for more memory) by at least
-  // 'bytes'. Returns false if not possible, true if the request succeeded. May allocate
-  // more memory than was requested.
-  // TODO: always returns false for now, not yet implemented.
-  bool ExpandLimit(int64_t /* unused: bytes */) { return false; }
-
   // Increases consumption of this tracker and its ancestors by 'bytes' only if
   // they can all consume 'bytes'. If this brings any of them over, none of them
   // are updated.