On Sat 11-09-21 04:23:24, Kirill A. Shutemov wrote: > On Fri, Sep 10, 2021 at 04:16:28PM -0400, Kent Overstreet wrote: > > So we should listen to the MM people. > > Count me here. > > I think the problem with folio is that everybody wants to read in her/his > hopes and dreams into it and gets disappointed when see their somewhat > related problem doesn't get magically fixed with folio. > > Folio started as a way to relief pain from dealing with compound pages. > It provides an unified view on base pages and compound pages. That's it. > > It is required ground work for wider adoption of compound pages in page > cache. But it also will be useful for anon THP and hugetlb. > > Based on adoption rate and resulting code, the new abstraction has nice > downstream effects. It may be suitable for more than it was intended for > initially. That's great. > > But if it doesn't solve your problem... well, sorry... > > The patchset makes a nice step forward and cuts back on mess I created on > the way to huge-tmpfs. > > I would be glad to see the patchset upstream. I do agree here. While points that Johannes brought up are relevant and worth thinking about I do also see a clear advantage of folio (or whatever $name) is bringing. The compound page handling is just a mess and source of practical problems and bugs. This really requires some systematic approach to deal with it. The proposed type system is definitely a good way to approach it. Johannes is not happy about having the type still refer to page units but I haven't seen an example where that leads to a worse or harder to maintain code so far. The evolution is likely not going to stop at the current type system but I haven't seen any specifics to prove it would stand in the way. The existing code (fs or other subsystem interacting with MM) is going to require quite a lot of changes to move away from struct page notion but I do not see folios to add fundamental blocker there. All that being said, not only I see folios to be a step into the right direction to address compound pages mess it is also a code that already exists and gives some real advantages. I haven't heard anybody subscribing to a different approach and providing an implementation in a foreseeable future so I would rather go with this approach then dealing with the existing code long term. -- Michal Hocko SUSE Labs
