Support disk buffering for read operations in pipe mount

[tcibinan]

Background

Currently, pipe mount has memory buffering for read operations. It allows to keep some data in memory and thus reduce a number of requests to an underlying storage. Only a limited amount of data is kept in memory for a single file handle. Once the file handle is closed, then the memory is freed.

Memory buffering improves performance a lot but does not cover all scenarios. A lot of time it is extremely efficient to use disk buffering as well.

Approach

Introduce support for disk buffering in pipe mount.