Introduce memory manager statistics

[stotko]

Features:

• Thread-safe MemoryManagerStatistic instance implemented as a singleton
• Per Device logging of memory allocations and frees
• Configurable print modes: All, Unbalanced, None
• Automatic print at the end of the program, defaults to Unbalanced to minimize noise

Detected memory leaks in unit tests:

• Skipped Free in LU decomposition when the operation fails

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This change is 

[update-docs]

Thanks for submitting this pull request! The maintainers of this repository would appreciate if you could update the CHANGELOG.md based on your changes.

[theNded]

Reviewed 4 of 5 files at r1.
Reviewable status: 4 of 5 files reviewed, 2 unresolved discussions (waiting on @stotko)

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cpp/open3d/core/MemoryManager.cpp, line 42 at r1 (raw file):

void* MemoryManager::Malloc(size_t byte_size, const Device& device) {
    MemoryManagerStatistic::getInstance().IncrementCountMalloc(device);

Shall we count byte_size as well? That might be helpful for more advanced checks.

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cpp/open3d/core/MemoryManagerStatistic.cpp, line 36 at r1 (raw file):

namespace core {

MemoryManagerStatistic& MemoryManagerStatistic::getInstance() {

Should we use GetInstance to keep consistency?

[stotko]

Reviewable status: 2 of 5 files reviewed, 2 unresolved discussions (waiting on @theNded)

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cpp/open3d/core/MemoryManager.cpp, line 42 at r1 (raw file):

Previously, theNded (Wei Dong) wrote…

Shall we count byte_size as well? That might be helpful for more advanced checks.

Done.

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cpp/open3d/core/MemoryManagerStatistic.cpp, line 36 at r1 (raw file):

Previously, theNded (Wei Dong) wrote…

Should we use GetInstance to keep consistency?

Done.

[theNded]

Reviewed 3 of 3 files at r2.
Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @theNded)

[yxlao]

Reviewed 2 of 5 files at r1, 2 of 3 files at r2.
Reviewable status: all files reviewed, 4 unresolved discussions (waiting on @stotko and @theNded)

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cpp/open3d/core/MemoryManager.cpp, line 50 at r2 (raw file):

void MemoryManager::Free(void* ptr, const Device& device) {
    GetDeviceMemoryManager(device)->Free(ptr, device);
    MemoryManagerStatistic::GetInstance().IncrementCountFree(device, ptr);

nit: shall we change the order to be consistent with MemoryManager::Free(ptr, device)?
i.e.

// We have:
MemoryManager::Free(ptr, device);
// Change IncrementCountFree to:
IncrementCountFree(ptr, device);

Similarly for IncrementCountMalloc:

// We have:
MemoryManager::Malloc(byte_size, device);
// Change IncrementCountMalloc to:
IncrementCountMalloc(ptr, byte_size, device);

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cpp/open3d/core/MemoryManagerStatistic.h, line 76 at r2 (raw file):

    };

    struct DeviceComparator {

This could be useful on other occasions if we'd like to use Device as the key in a map/unordered_map.

Shall we consider moving this to the Device class itself? For the unordered_map version, this would look like:

class Device {
public:
    struct Hash {
        std::size_t operator()(const open3d::core::Device& device) const {
            return std::hash<std::string>{}(device.ToString());
        }
    };
};

and, we can use the unordered_map as:

static std::unordered_map<Device, MemoryStatistics, Device::Hash>;

[stotko]

Reviewable status: 2 of 6 files reviewed, 3 unresolved discussions (waiting on @theNded and @yxlao)

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cpp/open3d/core/MemoryManager.cpp, line 50 at r2 (raw file):

Previously, yxlao (Yixing Lao) wrote…

nit: shall we change the order to be consistent with MemoryManager::Free(ptr, device)?
i.e.

// We have:
MemoryManager::Free(ptr, device);
// Change IncrementCountFree to:
IncrementCountFree(ptr, device);

Similarly for IncrementCountMalloc:

// We have:
MemoryManager::Malloc(byte_size, device);
// Change IncrementCountMalloc to:
IncrementCountMalloc(ptr, byte_size, device);

Done.

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cpp/open3d/core/MemoryManagerStatistic.h, line 76 at r2 (raw file):

Previously, yxlao (Yixing Lao) wrote…

This could be useful on other occasions if we'd like to use Device as the key in a map/unordered_map.

Shall we consider moving this to the Device class itself? For the unordered_map version, this would look like:

class Device {
public:
    struct Hash {
        std::size_t operator()(const open3d::core::Device& device) const {
            return std::hash<std::string>{}(device.ToString());
        }
    };
};

and, we can use the unordered_map as:

static std::unordered_map<Device, MemoryStatistics, Device::Hash>;

Done. FYI I used std::map<Device, MemoryStatistics> to have a consistent ordering during Print().