[lc-devel] [PATCH] 2.4.18-0.22

[Rodrigo S. de C. <rc...@im...>]

Hi all,

The new 0.22 version is out for 2.4.18 version of Linux Kernel. This
version has two main features: the whole page cache is supported, so
from now on all pages from page cache (not only swap cache pages) are
compressed; and manual adaptivity is fully implemented.

- Page Cache Support

These changes are not complex but took quite a while to accomplish a
good stability. Some prelimary tests with dbench and 0.22pre7 are
available at:

http://linuxcompressed.sourceforge.net/statistics/0.22pre7_dbench/

This code may still need some changes for a better performance (which
will be done as soon as kernprof patch is available for 2.4.18), but
the results from these tests are pretty better than the ones performed
with 0.21.

- Clean Pages Support + Pages Not Removed in Page Fault

All pages are compressed now, no matter they are clean or not. That
means that only dirty fragments (= compressed pages) are going to be
written out to the backing storage.

Another interesting feature introduced in this version is the one
which only removes the pages when it gets unmapped (the process dies,
the file is removed, etc) or when we are out of space in compressed
cache. Beforehand we always removed the fragment from compressed cache
when servicing a page fault.

- Manual Adaptivity

Now all main data structures (fragment hash table and vswap) are
correctly resized to support the new compressed cache size. You can do
that echoing the new number of pages to be used by compressed cache to
the following file: /proc/sys/vm/comp_cache/size. A cat in this file
will show the current number of pages reserved for compressed cache.

Kernel parameter and Config option are going to set the _initial_ (not
maximum) number of pages used by compressed pages, you will be able to
change this number whenever you want. Note: The compressed cache
cannot be disable yet, so a very small number of pages for compressed
cache may become a bottleneck depending on the scenario. An option to
disable the compressed cache on the fly is one of our high-priority
itens on our todo list.

- Other Features

This version also have shared memory support back, many cleanups and
bug fixes, simpler and much more documented code (mainly vswap) and
also a code more stable (with new allocation failure handling, for
instance).

- Stability 

I tested a lot this patch, running concurrently mmap001, fillmem and
changing compressed cache size. I also compiled several times the
Linux Kernel and had a hard time to make dbench stable, but finally
did. The last tests I ran were those first tests (mmap001, fillmem and
comp cache resize) for a period of over 12 hours trying to make the
system really short of memory (usual scenario to trigger annoying
bugs). The code passed it. Anyway, I'd like to hear reports about its
stability.

Detailed Change Log:

http://sourceforge.net/project/shownotes.php?release_id=79628

Download:

http://prdownloads.sourceforge.net/linuxcompressed/patch-comp-cache-2.4.18-0.22.bz2

Regards,
-- 
Rodrigo S. de Castro <rc...@im...>