Changeset 97928 in vbox for trunk/src/VBox/Additions/common/VBoxGuest

Timestamp:

Dec 31, 2022 1:23:33 AM (2 years ago)

Author:

vboxsync

Message:

Add/VBoxGuestR0LibPhysHeap.cpp: Modified the free list search to stop when it encounters a free block so large it will probably be quicker to just split it than hope to find a perfect-ish free list match.

File:

• trunk/src/VBox/Additions/common/VBoxGuest/lib/VBoxGuestR0LibPhysHeap.cpp (modified) (6 diffs)

trunk/src/VBox/Additions/common/VBoxGuest/lib/VBoxGuestR0LibPhysHeap.cpp

@@ -102 +102 @@
  */
 #define VBGL_PH_MAX_FREE_SEARCH         16
+
+/** Threshold to stop the block search if a free block is at least this much too big.
+ *
+ * May cause more fragmation (depending on usage pattern), but should speed up
+ * allocation and hopefully reduce cache trashing.
+ *
+ * Since we merge adjacent free blocks when we can, free blocks should typically
+ * be a lot larger that what's requested.  So, it is probably a good idea to
+ * just chop up a large block rather than keep searching for a perfect-ish
+ * match.
+ *
+ * Undefine this to disable this trick.
+ */
+#if defined(DOXYGEN_RUNNING) || 1
+# define VBGL_PH_STOP_SEARCH_AT_EXCESS   _4K
+#endif
 
 /** Threshold at which to split out a tail free block when allocating.
@@ -490 +506 @@
     VBGLPHYSHEAPBLOCK *pIter;
     int32_t            cLeft;
+#ifdef VBGL_PH_STOP_SEARCH_AT_EXCESS
+    uint32_t           cbAlwaysSplit;
+#endif
     int                rc;
 
@@ -498 +517 @@
     AssertStmt(cbSize > 0, cbSize = sizeof(void *));  /* avoid allocating zero bytes */
 
-
     rc = RTSemFastMutexRequest(g_vbgldata.mutexHeap);
     AssertRCReturn(rc, NULL);
@@ -508 +526 @@
      * there to be many blocks in the heap.
      */
-    cLeft  = VBGL_PH_MAX_FREE_SEARCH;
-    pBlock = NULL;
+#ifdef VBGL_PH_STOP_SEARCH_AT_EXCESS
+    cbAlwaysSplit = cbSize + VBGL_PH_STOP_SEARCH_AT_EXCESS;
+#endif
+    cLeft         = VBGL_PH_MAX_FREE_SEARCH;
+    pBlock        = NULL;
     if (cbSize <= PAGE_SIZE / 4 * 3)
     {
@@ -534 +555 @@
                         pFallback = pIter;
                     if (PAGE_SIZE - ((uintptr_t)(pIter + 1) & PAGE_OFFSET_MASK) >= cbSize)
+                    {
                         if (!pBlock || pIter->cbDataSize < pBlock->cbDataSize)
                             pBlock = pIter;
+#ifdef VBGL_PH_STOP_SEARCH_AT_EXCESS
+                        else if (pIter->cbDataSize >= cbAlwaysSplit)
+                        {
+                            pBlock = pIter;
+                            break;
+                        }
+#endif
+                    }
                 }
 
@@ -563 +593 @@
                 }
 
+#ifdef VBGL_PH_STOP_SEARCH_AT_EXCESS
+                if (pIter->cbDataSize >= cbAlwaysSplit)
+                {
+                    /* Really big block - no point continue searching! */
+                    pBlock = pIter;
+                    break;
+                }
+#endif
                 /* Looking for a free block with nearest size. */
                 if (!pBlock || pIter->cbDataSize < pBlock->cbDataSize)