In the memory-management subsystem, the term "mapping" refers to the
connection between pages in memory and their backing store — the file that
represents them on disk. One of the fundamental assumptions in the
kernel is that a given page in the page cache belongs to exactly one mapping.
But, as Miklos Szeredi explained in a plenary session at the 2017 Linux
Storage, Filesystem, and Memory-Management Summit, there are situations
where it would be desirable to associate the same page with multiple
mappings. Achieving this goal may not be easy, though.
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