Re: [RFC Patch] use MTRR for write combining if PAT is not available

[Thomas Schlichter <thomas.schlichter@web.de>]

Suresh Siddha wrote:
> > > There is no need to go through num_var_ranges etc.
> > 
> > Well I have to remember wich file added which MTRR entries. Because I have
> > to remove them if the file is being closed. Therefore I need an array of size
> > "num_var_ranges" (or MTRR_MAX_VAR_RANGES which is the uper bound).
> 
> No. the private data  for example can keep track of a struct containing
> mtrr number and ref count etc. Exporting var_ranges and going through
> var ranges elements in an array is not clean, especially when you are
> populating only one element.

OK, I should have written that num_var_ranges is neccessary if I do copy a
algorithm for exactly the same purpose from an other place. And I don't see
anything better in having a dynamically growing list that makes the operation
of incrementing MTRR entries an O(n) operation where it now is a O(1) operation.

Additionally, the worst case memory requirement would be
2*sizeof(int)*num_var_ranges, where it is now 1*sizeof(int)*num_var_ranges.

So for me, this would be a step back, but if you want this, you should additionally
change arch/x86/kernel/cpu/mtrr/if.c from where I reused the algorithm.

Regards,
  Thomas