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windowsmemoryheap-memoryallocatorfragmentation
Wololo
Wololo

Reputation: 1

Trying to visualyze Heap Fragmentation

Im trying to measure heap fragmentation, I will use this formula :

Fragmentation = 1 - (LargestFreeBlockAvailable / TotalFreeMemory)

The tricky part is to find the largest free blocks.

I have found this code which allow me to show all blocks in the heap : https://learn.microsoft.com/en-us/windows/win32/toolhelp/traversing-the-heap-list

I'm trying to create fragmentation allocating and deallocating larger and larger blocks :

std::allocator<char> alloc;
char * tmp = alloc.allocate(100);
    alloc.deallocate(tmp,100);
    tmp = alloc.allocate(200);
    alloc.deallocate(tmp,200);
    tmp = alloc.allocate(300);
    alloc.deallocate(tmp, 300);
    tmp = alloc.allocate(400);
    alloc.deallocate(tmp, 400);
    tmp = alloc.allocate(1000);
    alloc.deallocate(tmp, 1000);
    tmp = alloc.allocate(2000);
    alloc.deallocate(tmp, 2000);
    tmp = alloc.allocate(3000);
    alloc.deallocate(tmp, 3000);
    tmp = alloc.allocate(5000);
    alloc.deallocate(tmp, 5000);
    alloc.allocate(15000);

But I see no fragmentation when I run run the program, There is only one free block which correspond to the available memory left : Results

It's like if the block I freed previously where merged to this big last block... There arent any "hole" in the heap which would indicate fragmentation. Is anyone aware of the mechanism that occurs which avoid the fragmentation? Maybe im doing it wrong to create the fragmentation ?

Thank you in advance. Sorry for bad english.

Upvotes: 0

Views: 53

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