[$] Dueling memory-management performance regressions

The 2019 Linux Storage, Filesystem, and
Memory-Management Summit included a
detailed discussion about a memory-management fix that
addressed one performance regression while causing another. That fix,
which was promptly reverted, is still believed by most memory-management
developers to implement the correct behavior, so a
patch posted by Andrea Arcangeli in early May has relatively broad
support. That patch remains unapplied as of this writing, but the
discussion surrounding it has continued at a slow pace over the last
month. Memory-management subsystem maintainer Andrew Morton is faced with
a choice: which performance regression is more important?