Changeset 97918 in vbox for trunk/src/VBox/Additions

Timestamp:

Dec 30, 2022 3:59:06 PM (2 years ago)

Author:

vboxsync

Message:

Add/VBoxGuestR0LibPhysHeap.cpp: Use a fixed minimum size for splitting of a free node during allocation. This used to be the same as the allocation size, which typically results in more internal fragmentation that necessary.

File:

• trunk/src/VBox/Additions/common/VBoxGuest/lib/VBoxGuestR0LibPhysHeap.cpp (modified) (2 diffs)

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

@@ -91 +91 @@
 
 /** Threshold at which to split out a tail free block when allocating.
- * The value is the amount of user space, i.e. excluding the header.  */
+ *
+ * The value gives the amount of user space, i.e. excluding the header.
+ *
+ * Using 32 bytes based on VMMDev.h request sizes.  The smallest requests are 24
+ * bytes, i.e. only the header, at least 4 of these.  There are at least 10 with
+ * size 28 bytes and at least 11 with size 32 bytes.  So, 32 bytes would fit
+ * some 25 requests out of about 60, which is reasonable.
+ */
 #define VBGL_PH_MIN_SPLIT_FREE_BLOCK    32
 
@@ -485 +492 @@
         /* We have a free block, either found or allocated. */
 
-#if 1   /** @todo r=bird: This might work okay for medium sizes, but it can't be good for small
-         * allocations (unnecessary extra work) nor for large ones (internal fragmentation). */
-        if (pBlock->cbDataSize > 2 * (cbSize + sizeof(VBGLPHYSHEAPBLOCK)))
-#else
         if (pBlock->cbDataSize >= sizeof(VBGLPHYSHEAPBLOCK) * 2 + VBGL_PH_MIN_SPLIT_FREE_BLOCK + cbSize)
-#endif
         {
             /* Data will occupy less than a half of the block,