> > > + /*
> > > + * If the page has no mappings any more, just bail. An
> > > + * unmapped anon page is likely to be freed soon but worse,
> > > + * it's possible its anon_vma disappeared between when
> > > + * the page was isolated and when we reached here while
> > > + * the RCU lock was not held
> > > + */
> > > + if (!page_mapcount(page)) {
> > > + rcu_read_unlock();
> > > + goto uncharge;
> > > + }
> >
> > I haven't understand what prevent this check. Why don't we need following scenario?
> >
> > 1. Page isolated for migration
> > 2. Passed this if (!page_mapcount(page)) check
> > 3. Process exits
> > 4. page_mapcount(page) drops to zero so anon_vma was no longer reliable
> >
> > Traditionally, page migration logic is, it can touch garbarge of anon_vma, but
> > SLAB_DESTROY_BY_RCU prevent any disaster. Is this broken concept?
>
> The check is made within the RCU read lock. If the count is positive at
> that point but goes to zero due to a process exiting, the anon_vma will
> still be valid until rcu_read_unlock() is called.
Thank you!
then, this logic depend on SLAB_DESTROY_BY_RCU, not refcount.
So, I think we don't need your [1/11] patch.
Am I missing something?
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