High Frequency Heap

Question

Can anyone explain me the CLR's "HighFrequencyHeap"?

Answer 1

The high frequency heap is used to store commonly used internal data structures such as the method table of types. This can be verified using WinDbg/SOS as shown below.

It is also stated in the SSCLI book (p. 235).

Here's part of the output for !eeheap

--------------------------------------
Domain 1:          006428c0
LowFrequencyHeap:  00340000(2000:2000) Size: 0x2000 (8192) bytes.
HighFrequencyHeap: 00342000(8000:2000) Size: 0x2000 (8192) bytes.
StubHeap:          Size: 0x0 (0) bytes.
Virtual Call Stub Heap:
  IndcellHeap:     Size: 0x0 (0) bytes.
  LookupHeap:      Size: 0x0 (0) bytes.
  ResolveHeap:     Size: 0x0 (0) bytes.
  DispatchHeap:    Size: 0x0 (0) bytes.
  CacheEntryHeap:  Size: 0x0 (0) bytes.
Total size:        Size: 0x4000 (16384) bytes.
--------------------------------------
Jit code heap:
LoaderCodeHeap:    004e0000(10000:1000) Size: 0x1000 (4096) bytes.
Total size:        Size: 0x1000 (4096) bytes.
--------------------------------------
Module Thunk heaps:
Module 5ef21000: Size: 0x0 (0) bytes.
Module 00342e9c: Size: 0x0 (0) bytes.
Total size:              Size: 0x0 (0) bytes.
--------------------------------------
Module Lookup Table heaps:
Module 5ef21000: Size: 0x0 (0) bytes.
Module 00342e9c: Size: 0x0 (0) bytes.
Total size:              Size: 0x0 (0) bytes.
--------------------------------------
Total LoaderHeap size:   Size: 0x13000 (77824) bytes.
=======================================
Number of GC Heaps: 1
generation 0 starts at 0x02521018
generation 1 starts at 0x0252100c
generation 2 starts at 0x02521000
ephemeral segment allocation context: none
 segment     begin allocated  size
02520000  02521000  0252e010  0xd010(53264)
Large object heap starts at 0x03521000
 segment     begin allocated  size
03520000  03521000  03523250  0x2250(8784)
Total Size:              Size: 0xf260 (62048) bytes.
------------------------------
GC Heap Size:            Size: 0xf260 (62048) bytes.

Notice the location of the high frequency heap and the garbage collected heaps. Here's the output for !dumpobject for a statically allocated instance of Program.

0:000> !dumpheap -type Program
 Address       MT     Size
0252b630 00343858       12     
total 0 objects
Statistics:
      MT    Count    TotalSize Class Name
00343858        1           12 TestBench2010.Program
Total 1 objects
0:000> !do 0252b630 
Name:        TestBench2010.Program
MethodTable: 00343858
EEClass:     0034154c
Size:        12(0xc) bytes
File:        C:\workspaces\TestBench2010\TestBench2010\bin\Debug\TestBench2010.exe
Fields:
      MT    Field   Offset                 Type VT     Attr    Value Name
00343858  4000001        4 ...Bench2010.Program  0   static 0252b630 p
0:000> !dumpheap -type Program
 Address       MT     Size
0252b630 00343858       12     
total 0 objects
Statistics:
      MT    Count    TotalSize Class Name
00343858        1           12 TestBench2010.Program
Total 1 objects
0:000> !do 0252b630 
Name:        TestBench2010.Program
MethodTable: 00343858
EEClass:     0034154c
Size:        12(0xc) bytes
File:        C:\workspaces\TestBench2010\TestBench2010\bin\Debug\TestBench2010.exe
Fields:
  MT    Field   Offset                 Type VT     Attr    Value Name
00343858  4000001        4 ...Bench2010.Program  0   static 0252b630 p

Notice the address for the static reference p in the type Program. It points to an address in the garbage collected heap. Also, notice the address of the Method Table. It points to an address in the high frequency heap.