Re: Compressed Cache for NetBSD

[David Holland <dholland-tech%netbsd.org@localhost>]

On Thu, Sep 11, 2014 at 10:17:21PM -0400, vbhat%andrew.cmu.edu@localhost wrote:
 > I am a Masters student at Carnegie Mellon University specializing in
 > Systems (with special emphasis on Operating Systems and Storage Systems).
 > I have taken a class called Operating Systems Practicum
 > (https://www.cs.cmu.edu/~412/syllabus.html). The main objective of the
 > course is to add a feature to any Open Source systems-y product
 > (preferably an operating systems).
 > 
 > I was browsing through NetBSD project wiki and came across this really
 > interesting project of Compressed Cache
 > (http://wiki.netbsd.org/projects/project/compressed-cache/). I would
 > really appreciate if I could get some insights on this project status. I
 > will mostly be working alone on this project and the timeframe I have is
 > around 2 months.
 > 
 > I did some basic reading and have figured out that one approach to
 > implement this is to have a block device backed by kernel reserved memory.
 > This block device can used as a staging area for the compressed pages. The
 > interface can itself be provided through a VFS read/write semantics.
 > 
 > I would really appreciate if I could get any pointers and help on this
 > project. Eagerly awaiting a response.

I don't think anyone's already working on this.

Doing it with a block device (like the referenced Linux code)
shouldn't be all that difficult and even without much background
getting it done in a couple months is probably doable.

The drawback of doing it as a block device that you swap to is that
only anonymous memory pages will be sent to it; pages from files
(which includes e.g. program text) won't. But maybe that's good
enough; apparently the Linux world thought so.

(But don't try doing it inside uvm -- that is not a beginner project...)

-- 
David A. Holland
dholland%netbsd.org@localhost