Re: [PATCH RESEND v2] mm: Optional full ASLR for mmap() and mremap()

[Matthew Wilcox]

On Thu, Oct 08, 2020 at 07:13:51PM +0200, Jann Horn wrote:
> You may want to consider whether it would be better to store
> information about free memory per subtree in the VMA tree, together
> with the maximum gap size that is already stored in each node, and
> then walk down the tree randomly, with the randomness weighted by free
> memory in the subtrees, but ignoring subtrees whose gaps are too
> small.

Please, no.  We're trying to get rid of the rbtree, not enhance it
further.  The new data structure is a B-tree and we'd rather not burden
it with extra per-node information (... although if we have to, we could)

> And for expanding stacks, it might be a good idea for other
> reasons as well (locking consistency) to refactor them such that the
> size in the VMA tree corresponds to the maximum expansion of the stack
> (and if an allocation is about to fail, shrink such stack mappings).

We're doing that as part of the B-tree ;-)  Although not the shrink
stack mappings part ...