RE: VME driver patch for PowerPC

Cool. I was just about to suggest _PAGE_NO_CACHE | _PAGE_GUARDED.

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?

Daniel.

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Heater, Daniel (GE Infrastructure) wrote:

quoted

        /* 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

quoted

+       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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