CA-396124: amend criteria under which the garbage collector aborts

1. On the first iteration do not assess any of the failure criteria
2. Allow for two "grace" iterations, where the size is permitted to
grow and only consume those if the current size has grown more than
permitted from minimum achieved.

Signed-off-by: Mark Syms <mark.syms@cloud.com>

drivers/cleanup.py

@@ -1957,7 +1957,7 @@ def _coalesce(self, vdi):
         self.deleteVDI(vdi)
 
     class CoalesceTracker:
-        GRACE_ITERATIONS = 1
+        GRACE_ITERATIONS = 2
         MAX_ITERATIONS_NO_PROGRESS = 3
         MAX_ITERATIONS = 10
         MAX_INCREASE_FROM_MINIMUM = 1.2
@@ -1973,10 +1973,9 @@ def __init__(self, sr):
             self.startSize = None
             self.finishSize = None
             self.sr = sr
+            self.grace_remaining = self.GRACE_ITERATIONS
 
         def abortCoalesce(self, prevSize, curSize):
-            res = False
-
             self.its += 1
             self.history.append(self.HISTORY_STRING.format(its=self.its,
                                                            initSize=prevSize,
@@ -1993,33 +1992,38 @@ def abortCoalesce(self, prevSize, curSize):
             if prevSize < self.minSize:
                 self.minSize = prevSize
 
+            if self.its == 1:
+                # Skip evaluating conditions on first iteration
+                return False
+
             if prevSize < curSize:
                 self.itsNoProgress += 1
                 Util.log("No progress, attempt:"
                          " {attempt}".format(attempt=self.itsNoProgress))
                 util.fistpoint.activate("cleanup_tracker_no_progress", self.sr.uuid)
 
-            if (not res) and (self.its > self.MAX_ITERATIONS):
+            if self.its > self.MAX_ITERATIONS:
                 max = self.MAX_ITERATIONS
                 self.reason = \
                     "Max iterations ({max}) exceeded".format(max=max)
-                res = True
+                return True
 
-            if (not res) and (self.itsNoProgress >
-                              self.MAX_ITERATIONS_NO_PROGRESS):
+            if self.itsNoProgress > self.MAX_ITERATIONS_NO_PROGRESS:
                 max = self.MAX_ITERATIONS_NO_PROGRESS
                 self.reason = \
                     "No progress made for {max} iterations".format(max=max)
-                res = True
+                return True
 
             maxSizeFromMin = self.MAX_INCREASE_FROM_MINIMUM * self.minSize
-            if (self.its > self.GRACE_ITERATIONS and
-                (not res) and (curSize > maxSizeFromMin)):
-                self.reason = "Unexpected bump in size," \
-                              " compared to minimum achieved"
-                res = True
+            if curSize > maxSizeFromMin:
+                self.grace_remaining -= 1
+                if self.grace_remaining == 0:
+                    self.reason = "Unexpected bump in size," \
+                        " compared to minimum achieved"
+
+                    return True
 
-            return res
+            return False
 
         def printReasoning(self):
             Util.log("Aborted coalesce")

tests/test_cleanup.py

@@ -1299,14 +1299,17 @@ def test_leafCoalesceTracker(self):
         expectedHistory = [
             "Iteration: 1 -- Initial size 100 --> Final size 100",
             "Iteration: 2 -- Initial size 100 --> Final size 121",
+            "Iteration: 3 -- Initial size 100 --> Final size 141",
         ]
         expectedReason = "Unexpected bump in size," \
                          " compared to minimum achieved"
         res = tracker.abortCoalesce(100, 100)
         self.assertFalse(res)
         res = tracker.abortCoalesce(100, 121)
+        self.assertFalse(res)
+        res = tracker.abortCoalesce(100, 141)
         self.autopsyTracker(tracker, res, expectedHistory,
-                            expectedReason, 100, 121, 100)
+                            expectedReason, 100, 141, 100)
 
     def test_leafCoaleesceTracker_too_many_iterations(self):
         sr = create_cleanup_sr(self.xapi_mock)
@@ -1343,10 +1346,11 @@ def test_leafCoalesceTracker_getting_bigger(self):
             "Iteration: 1 -- Initial size 100 --> Final size 101",
             "Iteration: 2 -- Initial size 100 --> Final size 101",
             "Iteration: 3 -- Initial size 100 --> Final size 101",
-            "Iteration: 4 -- Initial size 100 --> Final size 101"
+            "Iteration: 4 -- Initial size 100 --> Final size 101",
+            "Iteration: 5 -- Initial size 100 --> Final size 101"
         ]
         expectedReason = "No progress made for 3 iterations"
-        self.exerciseTracker(tracker, 100, 101, 3, expectedHistory,
+        self.exerciseTracker(tracker, 100, 101, 4, expectedHistory,
                              expectedReason, 100, 101, 100)
 
     def runAbortable(self, func, ret, ns, abortTest, pollInterval, timeOut):