Re: vm issues (2)

[Andrea Arcangeli <andrea@suse.de>]

On Tue, Feb 25, 2003 at 01:13:28PM +0100, Dejan Muhamedagic wrote:
> Hello,
> 
> The new kernel 2.4.21-pre4aa3 is running now, but the box behaves
> similarly.  It still swaps quite a lot and much more than the rmap
> vm.  Both servers are under the same load.
> 
> One difference is the amount of free memory:
> 
>  r  b  w   swpd   free   buff  cache  si  so    bi    bo   in cs  us  sy  id
> aa:
>  0  7  0 5773620 202416 118076 2069716 5330 746  5330   766 4845 5597  12  14  74
> rmap:
>  0  0  0 3498044  13572   4144 4754596  74   0    75     6  642 598   5   3  92
> 
> The aa kernel keeps ~200MB out of 6GB of memory unused.  I'm not
> sure, but if we could reduce it perhaps there would be much less
> swapping.  Is there a way to achieve this?

that is a feature, it guarantees highmem unfreeable allocations like
pagetables can't eat all your normal zone. You can reduce the 200MB with
this boot command:

	lower_zone_reserve=256,256

As to decrease the swapping I just told you how to do that tweaking
vm_mapped_ratio.

> 
> Another notable difference between the two vm versions is that the
> rmap vm maintains about 80% of memory on the active list and the
> aa vm much less: between 4% and 12%.  The rmap vm must use more
> CPU, but these servers have a lot of processing power so it is not
> noticeable.

the theory was that rmap would reduce the cpu utilization but of course
the patch don't do juts rmap.

Andrea