Integrated: 8312132: Add tracking of multiple address spaces in NMT

[Johan Sjölen]

On Wed, 13 Mar 2024 21:52:58 GMT, Johan Sjölen <jsjolen at openjdk.org> wrote:

> Hi,
> 
> This PR introduces a new abstraction to NMT, named `MemoryFileTracker`. Today, NMT does not track any memory outside of the virtual memory address space. This means that if you allocated memory in something such as a memory-backed file and use `mmap` to map into that memory, then you'll have trouble reporting this to NMT. This is the situation that ZGC is in, and that is what this patch attempts to fix.
> 
> ## `MemoryFileTracker`
> 
> The `MemoryFileTracker` adds the ability of adding new virtual memory address spaces to NMT and committing memory to these, the basic API is:
> 
> ```c++
>     static MemoryFile* make_device(const char* descriptive_name);
>     static void free_device(MemoryFile* device);
> 
>     static void allocate_memory(MemoryFile* device, size_t offset, size_t size,
>                                 MEMFLAGS flag, const NativeCallStack& stack);
>     static void free_memory(MemoryFile* device, size_t offset, size_t size);
> 
> 
> It is easiest to see how this is used by looking at what ZGC's `ZNMT` class does:
> 
> ```c++
> void ZNMT::reserve(zaddress_unsafe start, size_t size) {
>   MemTracker::record_virtual_memory_reserve((address)start, size, CALLER_PC, mtJavaHeap);
> }
> void ZNMT::commit(zoffset offset, size_t size) {
>   MemTracker::allocate_memory_in(ZNMT::_device, static_cast<size_t>(offset), size, mtJavaHeap, CALLER_PC);
> }
> void ZNMT::uncommit(zoffset offset, size_t size) {
>   MemTracker::free_memory_in(ZNMT::_device, (size_t)offset, size);
> }
> 
> void ZNMT::map(zaddress_unsafe addr, size_t size, zoffset offset) {
>   // NMT doesn't track mappings at the moment.
> }
> void ZNMT::unmap(zaddress_unsafe addr, size_t size) {
>   // NMT doesn't track mappings at the moment.
> }
> 
> 
> As you can see, any mapping between reserved regions and device-allocated memory is not recorded in NMT. This means that in detailed mode you only get reserved regions printed for the reserved memory, the device-allocated memory is reported separately. When performing summary reporting any memory allocated via these devices is added to the corresponding `MEMFLAGS` as `committed` memory. 
> 
> This patch is also acting as a base on which we deploy multiple new backend ideas to NMT. These ideas are:
> 
> 1. Implement VMA tracking using a balanced binary tree approach. Today's `VirtualMemoryTracker`'s usage of linked lists is slow and brittle, we'd like to move away from it. Our Treap-based approach in this patch gives a performance boost such that we see 25x better performance in a benchmark. The idea and draft of this...

This pull request has now been integrated.

Changeset: 3944e673
Author:    Johan Sjölen <jsjolen at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/3944e67366601b6f748df1c5f93f184a7cb23ec3
Stats:     2357 lines in 21 files changed: 2252 ins; 86 del; 19 mod

8312132: Add tracking of multiple address spaces in NMT

Co-authored-by: Thomas Stuefe <stuefe at openjdk.org>
Reviewed-by: stefank, stuefe

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PR: https://git.openjdk.org/jdk/pull/18289