Unicorn memory usage improvement with Ruby 2.0.0

gistfile1.md

Unicorn memory usage improvement with Ruby 2.0.0

Here's a preliminary experiment to see how much memory is saved with the new copy-on-write friendly (bitmap marking) GC.

Calculated by memstats.rb https://gist.github.com/kenn/5105061 on Debian x86_64.

Master process:

# ./memstats.rb 20547
Memory Summary:
  private_clean                 448 kB
  private_dirty              24,492 kB
  pss                        28,278 kB
  rss                        73,144 kB
  shared_clean                4,520 kB
  shared_dirty               43,684 kB
  size                      184,120 kB
  swap                            0 kB

Worker process:

# ./memstats.rb 20554
Memory Summary:
  private_clean                   0 kB
  private_dirty              25,012 kB
  pss                        27,695 kB
  rss                        71,216 kB
  shared_clean                2,648 kB
  shared_dirty               43,556 kB
  size                      255,504 kB
  swap                            0 kB

rss represents the physical memory that is actually used, and it's comprised of private_clean + private_dirty + shared_clean + shared_dirty.

For the worker process, among 71,216 KB of physical memory, 46,204 KB is shared and 25,012 KB is private, that is, 65% of its memory is shared between workers and the master.

In other words, the footprint of a unicorn worker on this system is only 25MB instead of 70MB. I think it's a big deal!