On Wed, Sep 22, 2021 at 11:08:58AM -0400, Johannes Weiner wrote: > On Tue, Sep 21, 2021 at 05:22:54PM -0400, Kent Overstreet wrote: > > - it's become apparent that there haven't been any real objections to the code > > that was queued up for 5.15. There _are_ very real discussions and points of > > contention still to be decided and resolved for the work beyond file backed > > pages, but those discussions were what derailed the more modest, and more > > badly needed, work that affects everyone in filesystem land > > Unfortunately, I think this is a result of me wanting to discuss a way > forward rather than a way back. > > To clarify: I do very much object to the code as currently queued up, > and not just to a vague future direction. > > The patches add and convert a lot of complicated code to provision for > a future we do not agree on. The indirections it adds, and the hybrid > state it leaves the tree in, make it directly more difficult to work > with and understand the MM code base. Stuff that isn't needed for > exposing folios to the filesystems. > > As Willy has repeatedly expressed a take-it-or-leave-it attitude in > response to my feedback, I'm not excited about merging this now and > potentially leaving quite a bit of cleanup work to others if the > downstream discussion don't go to his liking. > > Here is the roughly annotated pull request: Thanks for breaking this out, Johannes. So: mm/filemap.c and mm/page-writeback.c - I disagree about folios not really being needed there. Those files really belong more in fs/ than mm/, and the code in those files needs folios the most - especially filemap.c, a lot of those algorithms have to change from block based to extent based, making the analogy with filesystems. I think it makes sense to drop the mm/lru stuff, as well as the mm/memcg, mm/migrate and mm/workingset and mm/swap stuff that you object to - that is, the code paths that are for both file + anonymous pages, unless Matthew has technical reasons why that would break the rest of the patch set. And then, we really should have a pow wow and figure out what our options are going forward. I think we have some agreement now that not everything is going to be a folio going forwards (Matthew already split out his slab conversion to a new type) - so if anonymous pages aren't becoming folios, we should prototype some stuff and see where that helps and hurts us. > As per the other email I still think it would have been good to have a > high-level discussion about the *legitimate* entry points and data > structures that will continue to deal with tail pages down the > line. To scope the actual problem that is being addressed by this > inverted/whitelist approach - so we don't annotate the entire world > just to box in a handful of page table walkers... That discussion can still happen... and there's still the potential to get a lot more done if we're breaking open struct page and coming up with new types. I got Matthew on board with what you wanted, re: using the slab allocator for larger allocations
