object/put: Use one data buffer per-request

Is your feature request related to a problem? Please describe.

ObjectService.Put devours a lot of memory for data buffers, sometimes excessively. Current scheme:

client ---> server OS |---> gRPC ---> [slicer] ---> ObjectService ---> storage

• node process cannot affect anything up to OS overall
• no slicer when object is "ready"

each stage component of the whole processing buffers the data. This leads to redundancy leading to memory overuse

Describe the solution you'd like

allocate single buffer for the whole operation

OS |---> [xxx__buffer__xxx] ---> storage

where, in general, storage are data drives that could be remote (depending on the client-defined storage policy)

The buffer size depends on the following factors:

• fixed amount of data specified by the client (undefined in general)
• optimal transmission unit of local and remote drives
• optimal transmission unit b/w all remote node connections
• MaxObjectSize
• current node state

node selects optimal buffer size and serves request within the allocated buffer. Then algorithm is simple:

• read buffer from

we can start from the simplest min(MaxObjectSize, PayloadSize | Inf) model and get rid of redundant data copies. This will already reduce resource consumption horizontally. Then we'll develop more adaptive models

Describe alternatives you've considered

not yet

Additional context

• #2686
• #2719

Start with pkg/services/object/put/distributed.go at the linked ObjectService.Put path, then read the related context in issues #2686 and #2719. Establish how the initial min(MaxObjectSize, PayloadSize | Inf) buffer model fits the request flow and how reduced copying would be verified; the issue does not name tests or a complete implementation boundary.