> rcu_unlock:
> +
> + /* Drop an anon_vma reference if we took one */
> + if (anon_vma && atomic_dec_and_lock(&anon_vma->migrate_refcount, &anon_vma->lock)) {
> + int empty = list_empty(&anon_vma->head);
> + spin_unlock(&anon_vma->lock);
> + if (empty)
> + anon_vma_free(anon_vma);
> + }
> +
Why don't we check ksm_refcount here? Also, why drop_anon_vma() doesn't
need check migrate_refcount?
plus, if we add this logic, we can remove SLAB_DESTROY_BY_RCU from
anon_vma_cachep and rcu_read_lock() from unmap_and_move(), I think.
It is for preventing anon_vma recycle logic. but no free directly mean
no memory recycle.
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