High committed memory but small heap size

Question

One of my app is reported to be using 5 gigs memory, when i took the dump of the process and analyze in windbg, i can see that the total committed size is 5 gigs as was reported, but then the total managed heap size is only 1.6 gigs.

Question: what could cause the commit size to be so big when heap size is only a few gigs, I could see the MEM_COMMIT size was almost all used by PAGE_READWRITE sections, could it be possibly memory fragmentation?

State Size MEM_COMMIT 5.653 Gb MEM_RESERVE 2.597 Gb

GC Heap Size: Size: 0x67cefd88 (1741618568) bytes.

Answer 1

Yes the commit size not accounted in managed heap could come from fragmentation in unmanaged heaps. The command !heap -s will display them in windbg. You may also use VMMap to quickly rule out other kind of memory allocated data.