Messages in this thread | | | Date | Mon, 15 Nov 2004 19:59:46 -0300 | From | Werner Almesberger <> | Subject | Re: [RFC] Generalize prio_tree (1/3) |
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Rajesh Venkatasubramanian wrote: > No, that's not possible. Whenever we change vm_pgoff, vm_start, or > vm_end, we reshuffle the prio_tree. Check mm/mmap.c:vma_adjust().
Excellent, that makes it a lot easier.
> If you are thinking vm_set.head or vm_set.parent is free to use > for h_index, then it is incorrect. No field is free. If a vma > is a tree node (and in this discussion we care only about tree > nodes), then every field in vma->shared is used. We cannot reuse > them for storing h_index.
Oh, I see. I thought it was that either vm_set or prio_tree_node was used. (Which I found somewhat confusing, but attributed my confusion to simply not understanding all the strange ways of MM.) Sorry about the confusion.
So yes, one more word then :-(
> If we impose that there can be only 2 types of prio_tree, then > we can simply add an if-else condition in the GET_INDEX macro. > IMHO, that will not lead to any noticeable performance drop.
Yes, that sounds better. It would also allow for a later transition of VMA_PRIO_TREE to GENERIC_PRIO_TREE.
Now, if we want to prepare things already now for a later migration, it would be nice to call the generic one "struct prio_tree_node", since it would eventually become the only node type anyway.
Perhaps something along these lines:
struct prio_tree_node { struct vma_prio_tree_node prio_tree_node; unsigned long r_index, h_index; };
Or would you consider this as premature optimization ?
> But, I agree with you that changing the layout of vm_area_struct > is a better (but intrusive) approach.
I also wonder how expensive the calculations in HEAP_INDEX are. Probably not very.
To make the intrusive change a bit more palatable, vm_pgoff could become #define vm_pgoff(vma) ((vma)->shared.prio_tree_node.r_index)
Okay, so now we only need someone who has meaningful MM tests to tell us how badly this would hurt performance :-)
Thanks, - Werner
-- _________________________________________________________________________ / Werner Almesberger, Buenos Aires, Argentina werner@almesberger.net / /_http://www.almesberger.net/____________________________________________/ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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