RetryFilter uses memory multiple times the size of incoming requests

[gzmrst]

Spring Cloud Gateway 4.2.0
Spring Boot 3.4.3

We have a gateway configured with a retry filter. The filter is configured to only retry on GET method calls, similar to the default config.
We have noticed that for POST calls, when the retry filter is present, lots of buffer memory is used.
If we remove the retry filter completely, then the memory usage drops significantly.
The buffer memory that gets allocated is significantly more than the size of the incoming request.

In our tests, when the incoming post was 500MB, then the memory used was around 2GB.

The problem is in three parts:

1. Too much buffer memory is allocated. Why does it need 4 times the file size allocated as a buffer?
2. and not all of it is released. The graph below shows the memory trending upwards after each call. Each request seems to allocate 2GB and then only releases 1.5GB. (This one I am not so sure about, perhaps GC would release some more memory eventually)
3. The memory is all allocated even if the filter is configured not to retry e.g. even if the method does not match the predicates.

Memory usage for POST requests when retry filter is active only for GET requests

Memory usage for POST request when retry filter is disabled

Retry Filter Config

        FilterDefinition retryFilterDef = new FilterDefinition();
        retryFilterDef.setName("Retry");
        retryFilterDef.addArg("retries", "3");
        //The default config for the methods is GET only. Added just to double check.
        retryFilterDef.addArg("methods", "GET");

Attached is a test case to show the memory usage. It logs some basic memory stats, but it's easier to just look in JVisualVM.

repro.zip