Recoverable Virtual Memory AOS Proj 4

Azat Khasanshin, Netra Kenkarey

1. How you use logfiles to accomplish persistency plus transaction semantics.

We use logfiles to store records of changes being made to mapped segments. If user program crashes,
data can be restored from these logfiles and backing files. This allows us to achieve persistency.
The changes are written to logfiles only when user calls rvm_commit_transaction. In case user program decides
to abort changes, initial values are restored from in-memory undo records. This allows us to achieve transaction semantics.

2. What goes in them? How do the files get cleaned up, so that they do not expand indefinitely?

For each call of rvm_about_to_modify we store:
    - segment name
    - offset
    - size
    - new data

Log files can be cleaned by calling rvm_truncate_log. This function goes through the changes and applies them to respective backing
files of each segment.