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I am writing an analysis application in C# that has to deal with a lot of memory. I use ANTS Memory Profiler 7.4 for optimizing my memory management. While doing so, I realized that all of my double[,] arrays I use (and i need them) are placed on the LOH although the largest of these arrays is about 24.000 bytes. Objects should not be put there before 85.000 bytes as far as I know. The problem is now, that since I have about several thousand instances of these double[,] arrays I have a lot of memory fragmentation (about 25% of my total memory usage is free memory that I can not use). some of these arrays stored on the LOH are even only 1.036 bytes in size. The problem is that sometimes I have to perform larger analysis and then I end up with an out of memory exception because of the massive memory loss due to LOH fragmentation.
Does anyone know why this is happening although it should not be a large object by definition?
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Large objects pose a special problem for the runtime: they can't be reliably moved by copying as they would require twice as much memory for garbage collection. Additionally, moving multi-megabyte objects around would cause the garbage collector to take an unreasonably long time to complete. .
If an object is greater than or equal to 85,000 bytes in size, it's considered a large object. This number was determined by performance tuning. When an object allocation request is for 85,000 or more bytes, the runtime allocates it on the large object heap.
Fragmentation is a state of the heap where free memory is available but not in a big enough consecutive memory space to host a new object about to be allocated.
It performs a blocking garbage collection of all generations. All objects, regardless of how long they have been in memory, are considered for collection; however, objects that are referenced in managed code are not collected. Use this method to force the system to try to reclaim the maximum amount of available memory.
The threshold size for putting arrays of doubles on the LOH is much lower than for other types. The reason for this is that items on the LOH are always 64-bit aligned, and doubles benefit greatly from being 64-bit aligned.
Note that this only affects programs running in 32 bits. Programs running in 64 bits have objects that are always aligned on a 64-bit boundary, so that LOH heuristic is not used for 64 bit programs.
The threshold size is 1000 doubles.
Also see https://connect.microsoft.com/VisualStudio/feedback/details/266330/
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