Re: Get rid of scan_control

[Marcelo Tosatti <marcelo.tosatti@cyclades.com>]

Hi Christoph,

On Thu, Feb 09, 2006 at 09:02:00PM -0800, Christoph Lameter wrote:
> This is done through a variety of measures:
> 
> 1. nr_reclaimed is the return value of functions and each function
>    does the summing of the reclaimed pages on its own.
> 
> 2. nr_scanned is passed as a reference parameter (sigh... the only leftover)
> 
> 3. nr_mapped is calculated on each invocation of refill_inactive_list. 
>    This is not that optimal but then swapping is not that performance 
>    critical.

But refill_inactive_list() is not used for swapping only. All evicted 
pages go through that path - it can be _very_ hot.

> 4. gfp_mask is passed as a parameter. OR flags to gfp_mask for may_swap 
>    and may_writepage.
> 
> 5. Pass swap_cluster_max as a parameter
> 
> Most of the parameters passed through scan_control become local variables.
> Therefore the compilers are able to generate better code.
> 
> And we do no longer have the problem of initializing scan control the
> right way.

I don't think its worth doing that - do you have any performance
measurement and analysis of the generated code? Is the current code a
bottleneck for any of your applications?

One very nice thing about "scan_control" is that it aggregates all
parameters related to reclaim procedure instances, making the code
much clearer, easier to understand, and elegant. Moreover it allows
expandability: new parameters can be contained within the structure.

At first, my opinion is that the possible benefits for performance do
not outweight the readability and expandability advantages it provides.

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>