Re: [RFC][PATCH 1/3] radix priority search tree - objrmap complexity fix

[Rajesh Venkatasubramanian <vrajesh@umich.edu>]

Hi Andrea,

There is a problem with the prio_tree merge. As usual it is
related to VM_NONLINEAR. When I was reading Hugh's nonlinear
patch, I recalled this problem.

Currently, with the prio_tree search in try_to_unmap, you will
not check all the nonlinear vmas. Earlier, with a list walk it
was not a problem. But, now in try_to_unmap we only select vmas
that map a given page. That's meaningless for nonlinear vmas.

I think the fix is straight-forward. My plan is to add a
"list_head i_mmap_nonlinear" to the address_space and use the
list to find all nonlinear vmas in try_to_unmap_inode.

In sys_remap_file_pages, we can do something like below:

if (!(vma->vm_flags & VM_NONLINEAR)) { /* vma is not already nonlinear */
	__vma_prio_tree_remove(&mapping->i_mmap_shared, vma)
	list_add_tail(&vma->shared.vm_set.list,
			&mapping->i_mmap_nonlinear);
}

Urggh. That forces us to take i_shared_sem in sys_remap_file_pages.

Please let me know if you have any better idea. Otherwise, tonite
I will send you a patch for 2.6.5-rc2-aa4.

Thanks,
Rajesh