Elasticsearch-net: RecyclableMemoryStreamManager does not ever release the allocated memory

[iderbyshev]

NEST/Elasticsearch.Net version: 7.3.1
RecyclableMemoryStreamManager allocates small memory blocks by request, but the logic of freeing up the allocated memory is never invoked.
MaximumFreeSmallPoolBytes is not set anywhere and has a default value of zero, so the blocks are always returned back to the pool:
https://github.com/elastic/elasticsearch-net/blob/2638c1e9963680abd566b5b599cfb9f5e1045d0f/src/Elasticsearch.Net/Providers/RecyclableMemoryStreamManager.cs#L330
This leads to the growing large objects heap under load.

[Mpdreamz]

Thank you for raising this we will do another dive into the pool characteristics especially for longer running processes

related: https://github.com/microsoft/Microsoft.IO.RecyclableMemoryStream/issues/75

[Mpdreamz]

Opened to https://github.com/elastic/elasticsearch-net/pull/4172 to be able to visualize the characteristics of the memory pool.

Closing this to keep the discussion isolated on the PR. Please don't hesitate to comment there 👍

[andreminelli]

There is any chance of these fixes get into v6.x? It's happening on release 6.8.1, too :(