Re: [LSF/MM TOPIC] Sharing file backed pages

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Wed, 2019-01-23 at 10:48 +0200, Amir Goldstein wrote:
> Hi,
> 
> In his session about "reflink" in LSF/MM 2016 [1], Darrick Wong
> brought up the subject of sharing pages between cloned files and the
> general vibe in room was that it could be done.

This subject has been around for a while.  We talked about cache
sharing for containers in LSF/MM 2013, although it was as a discussion
within a session rather than a session about it.  At that time,
Parallels already had an out of tree implementation of a daemon that
forced this sharing and docker was complaining about the dual caching
problem of their graph drivers.

So, what we need in addition to reflink for container images is
something like ksm for containers which can force read only sharing of
pages that have the same content even though they're apparently from
different files.  This is because most cloud container systems run
multiple copies of the same container image even if the overlays don't
necessarily reflect the origin.  Essentially it's the same reason why
reflink doesn't solve the sharing problem entirely for VMs.

James