Can reserved memory cause an Out Of memory exception
.net, memory, memory-management, out-of-memory, windbg
Solution
Yes, reserving memory can trigger `OutOfMemoryException`. Try allocating a couple of very large byte arrays. The memory for these will not be committed until you write to the content of the arrays. However, you can easily trigger OOM just by allocating these arrays.
I don't know the implementation details, but since VirtualAlloc will fail if it cannot honor a reserve request, I assume the CLR translates this into an exception. I don't see how it could turn a failed reserve request into anything useful, so an exception is a sensible choice.
Problem
We have a 32 bit windows service that leaks memory - OutOfMemory exception is thrown. It is .net 4.0 executable running on windows server 2003. While debugging crash dump files using WinDbg, I see that most of the memory is actually reserved and not commited. As you can see from WinDbg screenshot, there is 2.5 Gb of unclassified memory usage, and most of it 2.1 Gb is actually reserved memory (MEM_RESERVE). I have experience debugging crush dumps, but this scenario is something new to me. MEM_COMMIT is quit OK - 564.270 Mb, managed heap's size is abt 82 Mb I also checked native heaps to see, if there are big chunks of data preserved, but couldn't find anything suspicious there either So my question is - is it possible that MEM_RESERVED might result in OOM exception? If so, how can I debug it, see why/how huge amount of memory is being reserved? Where else would you look to find what might be the problem? If any other information is required please ask for it, and I will update my post.