swapspace layout improvements advocacy

[Tim Schmielau <tim@physik3.uni-rostock.de>]

On Wed, 12 Jan 2005, Andrew Morton wrote:

> Our current way of allocating swap can cause us to end up with little
> correlation between adjacent pages on-disk.  But this can be improved.  THe
> old swapspace-layout-improvements patch was designed to fix that up, but
> needs more testing and tuning.
> 
> It clusters pages on-disk via their virtual address.

2.6 seems in due need of such a patch.

I recently found out that 2.6 kernels degrade horribly when going into 
swap. On my dual PIII-850 with as little as 256 mb ram, I can easily 
demonstrate that by opening about 40-50 instances of konquerer with large 
tables, many images and such things. When the machine is into 80-120 mb of 
the 256 mb swap partition, it becomes almost unusable. Even the desktop 
background picture needs ~20sec to update, not to talk about any windows' 
contents. And you can literally hear the reason for it: the harddisk is 
seeking like crazy.

I've applied Ingo Molnars swapspace-layout-improvements-2.6.9-rc1-bk12-A1
port of the patch to a 2.6.11-rc1 kernel, and it handles the same workload 
much smoother. It's slow, but you can work with it.

I just wonder why noone else complained yet. Are systems with tight memory 
constraints so uncommon these days?

Tim