Minor optimisation to the heap manager for performance enhancement.

Detail:
  When splitting a free block in order to satisfy an allocation request,
    don't split if the remaining free space falls below a specified
    threshold (<= 8 bytes) to avoid creating lots of tiny free blocks,
    but instead gift the extra 8 bytes to the newly allocated block.
    This should stop the worst case heap fragmentation seen with OS_Heap
    heaps (particular the Toolbox's dynamic area).
Admin:
  Tested in Ursula desktop build.


Version 5.44. Tagged as 'Kernel-5_44'

VersionASM

@@ -11,14 +11,14 @@
                         GBLS    Module_HelpVersion
                         GBLS    Module_ComponentName
                         GBLS    Module_ComponentPath
-Module_MajorVersion     SETS    "5.43"
-Module_Version          SETA    543
+Module_MajorVersion     SETS    "5.44"
+Module_Version          SETA    544
 Module_MinorVersion     SETS    ""
-Module_Date             SETS    "25 May 2001"
-Module_ApplicationDate2 SETS    "25-May-01"
-Module_ApplicationDate4 SETS    "25-May-2001"
+Module_Date             SETS    "05 Jun 2001"
+Module_ApplicationDate2 SETS    "05-Jun-01"
+Module_ApplicationDate4 SETS    "05-Jun-2001"
 Module_ComponentName    SETS    "Kernel"
 Module_ComponentPath    SETS    "RiscOS/Sources/Kernel"
-Module_FullVersion      SETS    "5.43"
-Module_HelpVersion      SETS    "5.43 (25 May 2001)"
+Module_FullVersion      SETS    "5.44"
+Module_HelpVersion      SETS    "5.44 (05 Jun 2001)"
                         END

VersionNum

-/* (5.43)
+/* (5.44)
  *
  * This file is automatically maintained by srccommit, do not edit manually.
  *
  */
-#define Module_MajorVersion_CMHG        5.43
+#define Module_MajorVersion_CMHG        5.44
 #define Module_MinorVersion_CMHG        
-#define Module_Date_CMHG                25 May 2001
+#define Module_Date_CMHG                05 Jun 2001
 
-#define Module_MajorVersion             "5.43"
-#define Module_Version                  543
+#define Module_MajorVersion             "5.44"
+#define Module_Version                  544
 #define Module_MinorVersion             ""
-#define Module_Date                     "25 May 2001"
+#define Module_Date                     "05 Jun 2001"
 
-#define Module_ApplicationDate2         "25-May-01"
-#define Module_ApplicationDate4         "25-May-2001"
+#define Module_ApplicationDate2         "05-Jun-01"
+#define Module_ApplicationDate4         "05-Jun-2001"
 
 #define Module_ComponentName            "Kernel"
 #define Module_ComponentPath            "RiscOS/Sources/Kernel"
 
-#define Module_FullVersion              "5.43"
-#define Module_HelpVersion              "5.43 (25 May 2001)"
+#define Module_FullVersion              "5.44"
+#define Module_HelpVersion              "5.44 (05 Jun 2001)"

s/HeapMan

@@ -109,6 +109,16 @@ freblksize #    0
 ; They must also be capable of storing a 4 byte size field while allocated.
 ; This field is used to size the block to free when FreeArea is called.
 
+; This is the threshold for minimum heap block fragmentation size.  Splitting a
+; free block won't leave a free block which is <= than the size declared here.
+; If by choosing to use a particular free block, allocating a new block would
+; leave a free block of this size or less, add it on to the original size request
+; to avoid generating lots of silly little blocks that slow things down so much.
+; This value must not be too large because non-C callers may extend the block
+; piecemeal based on their (now wrong) knowledge of the block size.  The C library
+; reads the block size straight out of the heap block data, and will thus not
+; be fooled.
+minheapfragsize # 8
 
         ALIGN
 
@@ -605,6 +615,14 @@ garloop
         SUBS    HpTemp, HpTemp, size        ; In case this works, for below split
         BLO     garloop
 
+;
+; Try and stop very small blocks appearing due to fragmentation - if we fitted with
+; a minimal amount of overhead, pretend we had an exact match
+;
+        CMPNE   HpTemp, #minheapfragsize+1  ; set LO if we can salvage this tiny block
+        ADDLO   size, size, HpTemp          ; increment the size to encompass the block
+        MOVLOS  HpTemp, #0                  ; pretend we fitted exactly, set EQ
+
 ; Now addr -> a block on the free space list that our item will fit in
 ; If we have an exact fit (or as close as the granularity of the free list will
 ; allow), unlink this block and return it