On Mon, Nov 14, 2005 at 10:28:38AM -0800, Nitin Gupta wrote:
| Hi,
|    I've been working on porting the 'compressed cache' feature
| (http://linuxcompressed.sourceforge.net/ - feature explained in first few 
lines)
| to linux 2.6 kernel.
|   I'm wondering why this project is dead even when it showed great
| performance improvement when system is under memory pressure.

While it sounds interesting from an academic point of view, I wonder
how relevant this work (and any work related to paging) is when memory
can be purchased for under $200 a gigabyte. This is a different perspective
than Linux which is in common use on older machines and smaller machines
(even embedded systems) with small memories -- Solaris typically runs on
servers requiring a specified response time. Solaris users usually
consider it a *failure mode* when a system starts paging since its
response time becomes non-linearly poor and unpredictable!

Hence, I don't think this or any paging related projects will generate a
lot of interest in Solaris.

| Are there any serious drawbacks to this?
| Do you think it will be of any use if ported to solaris kernel?

As far as I can see, this is nearly impossible to port to Solaris, which
unlike Linux allows direct mapping of pages in the page cache.  Keeping
compressed data pages around in memory would also require having a better
idea of candidate pages to pageout than we can achieve on SPARC CPUs
since these CPUs do not have hardware support for ref/mod bits (making
paging candidate determination very costly). ZFS is very fast (being copy-
on-write it does sequential I/Os whereas swapfs does random disk access),
and it supports compression. ZFS is already slated to become the new
replacement to swapfs in the near future.

-- 
Eric Lowe       Solaris Kernel Development              Austin, Texas
Sun Microsystems.  We make the net work.                x64155/+1(512)401-1155
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