Re: [lc-devel] hello

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

Hi there!

On Sat, May 17, 2003 at 10:06:47PM +0200, Bob Arctor wrote:
> i patched 2.4.21rc2-ac2 , there were few trivial rejects, i didn't
> fixed only the ones in swapfile.c (i assume they're important when
> something is wrong with swap)
> 
> i disabled "support for page cache compression" , compiled and booted.
> it works!

Great!

> i'll install this kernel on my firewall too, which is only non-smp
> machine left :>
> 
> btw. what are problems with making patch (or at least parts of it)
> SMP-able?  i use openmosix patch making cluster out of few
> single-cpu machines, and on oM group
> (ope...@li...) one of programmers got
> information about your patch recently, but never readed it (some
> other user posted question wheter this and few others could be
> merged into oM)

I am very glad to hear that they talked about my patch in the
openmosix mailing list. :-) To answer your question about what are the
problems, I would say that the major problem now is time. As soon as I
can get enough time (or I get help from other programmers), it will be
done. Besides the bug you hit with loop device + swap file and a few
bugs, to check and improve SMP support it one of the top items on my
todo list.

> i think at least swap compression support could be merged in.
> 
> btw. performance - my laptop is a bit more responsive, stats show
> about 50% compression ratio and lot of pages compressed.  one of
> good things is that when it spins up disk (it is usually off) to
> swap something in/out it doesn't 'freeze' system for time disk isn't
> available.  i think it's because of grouping of swapout requests and
> compressing them before swapping out (so instead of swap out some of
> memory is just compressed waiting for disk to spin up, and then
> -when disk is available-swapped out)

A compressed cache that stores only pages backed by swap may improve
your system in a number of scenarios, but not in as many as if we have
page cache support. That is why I suggest you to test comp cache with
page cache support when it is finally stable with swap files.

BTW, I took a little longer to answer because first I wanted to
perform some tests. I found out that there is a bug with swapfile
support, because I guess comp cache code has never been tested with
swap files, only with swap partitions. As soon as I created a swap
file and ran with it, I hit some deadlocks. One is pretty obvious
(shame on me!) and I will fix it asap (now I have to think a little
how to solve it).

> about swapfile - thanks for hint, 
> swapon swapfile.img works. 
> ofcourse i tested 2.4.21-rc2-ac2-cc with swap via /dev/loop0 before i 
> switched to more robust swap method :)

Cool, it is a nicer solution that avoids the loop device overhead.

Regards,
-- 
Rodrigo