Re: VME driver patch for PowerPC

[Oliver Korpilla <okorpil@fh-landshut.de>]

Heater, Daniel (GE Infrastructure) wrote:
>>         /* Don't swap these pages out
>>          */
>>-       vma->vm_flags |= VM_RESERVED;
>>+       vma->vm_flags |= VM_LOCKED | VM_IO | VM_SHM;
>
>
> I'm trying to understand this change. VM_IO looks like it needs to
> be there to prevent deadlocks on core dumps.
> http://www.uwsg.iu.edu/hypermail/linux/kernel/0202.0/1309.html
>
> and if I'm interpreting some older mailing list postings correctly,
> VM_RESERVED is a replacement for VM_LOCKED | VM_SHM but VM_RESERVED
> may yield some performance advantages. Thus, in later kernels you
> only see VM_RESERVED and not VM_LOCKED | VM_SHM.
>
> Maybe since this is an out of tree driver, it should have
>
>>+       vma->vm_flags |= VM_LOCKED | VM_IO | VM_SHM | VM_RESERVED;
>
>
> to handle older kernels and still get the advantages of VM_RESERVED
> on newer kernels.
>
> What do you think? Am I interpreting this correctly?
>

To be frank, I "modelled" this after the flag configuration in
pci_mmap_page_range() in the PowerPC tree of kernel 2.4.21 (where I got the page
protection changes, too).

If VM_RESERVED is somewhat of an alias, it should prove okay. Looking into my
"documentation" yielded no quick results for flag interpretation.

I could simply test, if both works.

With kind regards,
Oliver Korpilla

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