Re: [PATCH v4] mm: Add MREMAP_DONTUNMAP to mremap().

Brian Geffon
2020-02-13T18:21:14Z

Hi Kirill,

> But if you do the operation for the VM_LOCKED vma, you'll have two locked
> VMA's now, right? Where do you account the old locked vma you left behind?

You bring up a good point. In a previous iteration of my patch I had
it clearing the locked flags on the old VMA as technically the locked
pages had migrated. I talked myself out of that but the more I think
about it we should probably do that. Something along the lines of:

+ if (vm_flags & VM_LOCKED) {
+ /* Locked pages would have migrated to the new VMA */
+ vma->vm_flags &= VM_LOCKED_CLEAR_MASK;
+ if (new_len > old_len)
+ mm->locked_vm += (new_len - old_len) >> PAGE_SHIFT;
+ }

I feel that this is correct. The only other possible option would be
to clear only the VM_LOCKED flag on the old vma leaving VM_LOCKONFAULT
to handle the MCL_ONFAULT mlocked situation, thoughts? Regardless I'll
have to mail a new patch because that part where I'm incrementing the
mm->locked_vm lost the check on VM_LOCKED during patch versions.

Thanks again for taking the time to review.

Brian