Re: [RFC Patch] use MTRR for write combining if PAT is notavailable

[Suresh Siddha]

On Thu, 2009-10-22 at 05:08 -0700, Thomas Schlichter wrote:
> When forking, what happens with the "struct file"? If it is being copied, then the
> processes share the same private data which would be freed during the first
> release(). I think this would be a problem whereever file-private data are used.
> 
> So I think it must be shared between the forked processes and some reference
> counting must exist. This reference counting must ensure that release() is only
> called when all processes did close() their file.
> 
> And in that case (shared "struct file", one single release() call in the end) this
> implementation should be completely safe...

I am referring to the refcount getting incremented. Also, let me think
about your direction (as the pci_mmap_page_rane() is explicitly adding
the mtrr, we should perhaps do the ref counting there, perhaps)

> > 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.

thanks
suresh

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