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wrote: > > > MADV_UNSHARE we implemented simply took a range and one could apply it to > > > the full process by supplying the full range. > > > > > > But yeah, the downside in any case is that you lose > > > > You just lose? :P I assume you forgot to finish this thought :>) > > "you lose the memory savings of COW" -- was still tired there. You and me both, bud... :) And right, yes agreed. > > > > > I wonder from rmap point of view whether you could actually simply check to > > see if you're fully CoW'd. > > > > E.g.: > > > > madvise(..., MADV_ISOLATE_COWED) > > > > And have it take the anon_vma write lock from root, have it walk the rmap, > > go and check to see if every folio in the VMA is now CoW'd, and if so, > > detatch the CoW'd anon_vma from its parent/root? > > TBH, this all feels like things we should be optimizing internally somehow. > > And don't get me started on > > MADV_ISOLATE_COWED eww > > NO_COWS eww > > COW NOW eww Holy CoW! ;) Yeah it'd be nice for us to do this automagically. But I suspect anything like this will be quite painful. A kthread to do this... hmmm... Doing it on fault? Expensive. Tracking it? Also expensive. ++lorenzos_grand_rework_goals I guess... > > > > > This would be a sort of after-the-fact thing, but maybe could be done > > periodically. > > > > Of course then if you had one folio that was not yet CoW'd, that'd prevent > > this from completing. > > [...] > > > > > > > > > Another point in favour of COW_NOW or EAGER_COW is that we can choose to > > > > allocate folios of the appropriate size at that time. Unless something's > > > > changed, I think we always COW individual pages rather than multiple > > > > pages at once. > > > > > > Yes. khugepaged will soon starting fixing that up later asynchronously I > > > hope. > > > > But only at mTHP granularity a. once the relevant series lands and b. if > > mTHP is enabled (I mean for sub-PMD sized/aligned ranges) :>) > > Well, we need khugepaged in one form or the other form mTHP in any case :P > > And the glorious future will have all sizes enabled as default. I look forward to this glorious future :) > > -- > Cheers > > David / dhildenb > > Cheers, Lorenzo