Poettering: Revisiting how we put together Linux systems

Posted Sep 9, 2014 11:23 UTC (Tue) by alexl (subscriber, #19068)
In reply to: Poettering: Revisiting how we put together Linux systems by mezcalero
Parent article: Poettering: Revisiting how we put together Linux systems

> And the file-level de-dup is not only important to ensure that you can
> share the data on disk, but also later on in RAM.

This is unfortunately not true. The files on each btrfs subvolume have a per-subvolume st_dev (different minor nr), and the page-cache is per-device. So, block sharing between btrfs volumes is strictly an on-disk thing, they will be cached separately in RAM.

I know this because I wrote the btrfs docker backend hoping to get this feaure (among others), and it didn't work.