have MinimumFreeSize take precedence over the low usage threshold

internal/core/logic.go

@@ -106,6 +106,15 @@ func checkReason(res db.Resource, asset db.Asset, reason db.OperationReason) *ui
 				}
 			}
 
+			//ALSO the MinimumFreeSize takes precedence over the low threshold: we're
+			//allowed to go into low usage if it helps us satisfy the MinimumFreeSize
+			if res.MinimumFreeSize != nil && asset.AbsoluteUsage != nil {
+				minSize := *res.MinimumFreeSize + *asset.AbsoluteUsage
+				if lowSize < minSize {
+					lowSize = minSize
+				}
+			}
+
 			if lowSize > 0 {
 				c.forbidAbove(lowSize)
 			}

internal/tasks/asset_scrape_test.go

@@ -1119,7 +1119,7 @@ func TestResizesEndingUpInLowThreshold(baseT *testing.T) {
 		t.ExpectPendingOperations(c.DB /*, nothing */)
 		t.ExpectFinishedOperations(c.DB /*, nothing */)
 
-		//BUT when we're inside the high/critical threshold, a downsize should be
+		//BUT when we're inside the high/critical threshold, an upsize should be
 		//generated even though upsizing puts us below the low threshold -- the
 		//idea being that it's better to be slightly too large than slightly too
 		//small
@@ -1141,6 +1141,37 @@ func TestResizesEndingUpInLowThreshold(baseT *testing.T) {
 	})
 }
 
+func TestUpsizeBecauseOfMinFreeSizePassingLowThreshold(baseT *testing.T) {
+	t := test.T{T: baseT}
+	forAllSteppingStrategies(t, func(c *Context, res db.Resource, setAsset func(plugins.StaticAsset), clock *test.FakeClock) {
+
+		//test that min_free_size takes precedence over the low usage threshold: we
+		//should upsize the asset to guarantee the min_free_size, even if this puts
+		//usage below the threshold
+		t.MustExec(c.DB, `UPDATE resources SET min_free_size = 2500`)
+		if !res.SingleStep {
+			//for percentage-step resizing, we need to set the size step comically
+			//large because we need to get below the low usage threshold to actually
+			//trigger the condition we want to test
+			t.MustExec(c.DB, `UPDATE resources SET size_step_percent = 200`)
+		}
+
+		clock.StepBy(10 * time.Minute)
+		t.Must(c.ScrapeNextAsset("foo", c.TimeNow()))
+
+		t.ExpectPendingOperations(c.DB, db.PendingOperation{
+			ID:           1,
+			AssetID:      1,
+			Reason:       db.OperationReasonHigh,
+			OldSize:      1000,
+			NewSize:      3000,
+			UsagePercent: 50,
+			CreatedAt:    c.TimeNow(),
+		})
+		t.ExpectFinishedOperations(c.DB /*, nothing */)
+	})
+}
+
 func ifthenelseF64(cond bool, thenValue float64, elseValue float64) float64 {
 	if cond {
 		return thenValue