odd scrolling issue in vim

[Chris Snook]

Jack Howarth wrote:
>    Has anyone else noticed this issue under Fedora 9 x86_64
> with the 2.6.25.10 or 2.6.26 kernels? I find that if I open
> a large text file in vim (as vi), jump to the bottom of the
> file and then use the 'k' metakey to scroll up that the scrolling
> is not smooth like in earlier Fedora releases. There is a huge
> lag in the process of scrolling up. Oddly scrolling down the file
> seems to be pretty smooth. This bug is really annoying. I assume
> it must be a vim bug.
>                Jack
> 

When you're scrolling down, the kernel does readahead, so it's fast. 
When you're scrolling up, it's pretty much all demand paging, so it's 
going to disk each time.  The difference is probably related to how the 
kernel is managing the memory on your workload.  I suspect that in the 
past it was paging in large chunks (see the vm.page-cluster sysctl) on 
each disk read, so it was still reading faster than you could notice the 
lag, and for some reason it has decided that's no longer a good idea due 
to memory pressue.  I haven't noticed this problem on my F9 x86_64 system.

-- Chris