Subject: Re: compressed device layer
To: None <dlagno@mail.nnov.ru>
From: Bill Studenmund <wrstuden@netbsd.org>
List: tech-kern
Date: 04/26/2004 10:34:07
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On Mon, Apr 26, 2004 at 05:46:11PM +0400, dlagno@mail.nnov.ru wrote:
>=20
> > I wonder if a compressed file system would be a better/easier/more
> > flexible aproach
>=20
> No doubt that compressed file system (or ffs with integrated compression)=
=20
> can achieve more compression ratio and can be more efficient.  But I=20
> doubt it is easier.  I consider high quality implementation of compressed=
=20
> filesystem an unmanagable task for myself currently.

I'd suggest looking at layered file systems. With a compressing layer, all=
=20
you have to do is focus on the compression and being a pager that=20
supplies/compresses the data.

Note that since we have UBC, all file data goes into and comes out of file=
=20
systems via the VM page cache.

There are some cache issues you will eventually need to think about, but=20
they only come up in low-memory situations and if someone tries to read=20
the compressed file. The low-memory issues will be there for cgd and for=20
any form of compression you do.

Take care,

Bill

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