poolmanager: Fix full pool detection for WASS

When a file cannot fit within the free plus removable space without
crossing the pool gap, a pool is considered full. WASS erroneously
used the decayed removable space in this check. This meant that
if all pools had very fresh files, they could all be considered
full even though there are plenty of removable files. This patch
changes the check to consider all removable space of a pool. The
decayed removable space is only used when weighting the random
selection.

Target: trunk
Request: 2.11
Request: 2.10
Request: 2.9
Request: 2.8
Request: 2.7
Request: 2.6
Ticket: http://rt.dcache.org/Ticket/Display.html?id=8390
Require-notes: yes
Require-book: no
Acked-by: Christian Bernardt <christian.bernardt@desy.de>
Patch: https://rb.dcache.org/r/7531/
(cherry picked from commit 42e31b5)

modules/dcache/src/main/java/org/dcache/poolmanager/WeightedAvailableSpaceSelection.java

@@ -185,17 +185,20 @@ protected double getAvailable(PoolCostInfo.PoolSpaceInfo space, long filesize)
     {
         long free = space.getFreeSpace();
         long gap = space.getGap();
+
+        /* If the pool cannot hold the file without eating into the gap, the
+         * pool is considered full.
+         */
+        if (free + space.getRemovableSpace() - filesize <= gap) {
+            return 0;
+        }
+
         double removable = getAvailableRemovable(space);
 
         /* The amount of available space on a pool is the sum of
          * whatever is free and decayed removable space.
          */
-        double available = free + removable;
-
-        /* If available space is less than the gap then the pool is
-         * considered full.
-         */
-        return (available - filesize > gap) ? available : 0;
+        return free + removable;
     }
 
     protected int getWriters(PoolCostInfo info)

modules/dcache/src/test/java/org/dcache/poolmanager/WeightedAvailableSpaceSelectionTest.java

@@ -105,4 +105,33 @@ public void testIdleFullPoolDoesNotAffectLoadNormalization()
                                             Functions.<PoolCostInfo>identity());
         assertThat(selected, is(busy));
     }
+
+    @Test
+    public void testYoungLruDoesNotPreventPoolSelection()
+    {
+        int total = 100_000_000;
+        int free = 100;
+        int precious = 0;
+        int removable = 1_000_000;
+        int lru = 10;
+        double breakEven = 0.5;
+        int gap = 1000;
+        double moverCostFactor = 0.5;
+        int moverActive = 0;
+        int moverMaxActive = 10;
+        int moverQueued = 0;
+        int moverReaders = 0;
+        int moverWriters = 0;
+        int filesize = 1000;
+
+        PoolCostInfo info = new PoolCostInfo("pool");
+        info.setSpaceUsage(total, free, precious, removable, lru);
+        info.getSpaceInfo().setParameter(breakEven, gap);
+        info.setMoverCostFactor(moverCostFactor);
+        info.addExtendedMoverQueueSizes("movers", moverActive, moverMaxActive, moverQueued, moverReaders, moverWriters);
+        PoolCostInfo selected =
+                wass.selectByAvailableSpace(singletonList(info), filesize,
+                                            Functions.<PoolCostInfo>identity());
+        assertThat(selected, is(info));
+    }
 }