Re: Get rid of scan_control

[Christoph Lameter <clameter@engr.sgi.com>]

On Sun, 12 Feb 2006, Nick Piggin wrote:

> I agree with Marcelo, I prefer scan_control. I'm not sure if it was
> modelled on writeback_control or not, but it is certianly very different:
> writeback_control is spread over many files and subsystems. scan_control
> is vmscan local and is simply used to alleviate the passing of many
> values back and forth between vmscan functions.

The trouble with scan_control is that it contains diverse variables. For 
example it caches nr_mapped, its used to pass results back to the caller 
etc. 

> Luckily there are very limited call stacks which modify this stuff so it isn't
> too hard to keep all in your head at once after you start doing a bit of work
> in vmscan. That said, we could implement a commenting convention to help
> things.
> 
> /*
>  * refill_inactive_list
>  * input:
>  * sc.nr_scan - specifies the number of ...
>  * sc.blah ...
>  *
>  * modifies:
>  * sc.nr_scan - blah blah
>  */

Could we at least pass the number of pages reclaimed back as the return 
value of the functions? I believe most of the savings that Andrew saw was 
due to the number of reclaimed pages being processed directly in 
registers.

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