[Libguestfs] [PATCH libnbd v3 0/3] copy: Preserve the host page cache.

[Richard W.M. Jones]

This is a combination and evolution of two previous series:

  https://listman.redhat.com/archives/libguestfs/2021-February/msg00091.html
  https://listman.redhat.com/archives/libguestfs/2021-February/msg00094.html

I made a few enhancements:

 - Separate macros for the platforms where we enhance reading
   (#ifdef PAGE_CACHE_MAPPING), vs writing (#ifdef EVICT_WRITES).
   This was mainly about renaming stuff.

 - When writing we now use 8 windows instead of 2 [both per thread].
   This reduces the overhead from about 25% to about 10%.  It's
   possible to reduce it further by using more windows, but you trade
   the amount of cruft added to the page cache.

 - This patch series is much more well-tested than before, including
   combining it with TLS, and testing it from the nbdkit test suite.

Rich.