On 7/24/2023 5:04 PM, Ryan Roberts wrote: > On 23/07/2023 13:33, Yin, Fengwei wrote: >> >> >> On 7/20/2023 5:41 PM, Ryan Roberts wrote: >>> Hi All, >>> >>> As discussed at Matthew's call yesterday evening, I've put together a list of >>> items that need to be done as prerequisites for merging large anonymous folios >>> support. >>> >>> It would be great to get some review and confirmation as to whether anything is >>> missing or incorrect. Most items have an assignee - in that case it would be >>> good to check that my understanding that you are working on the item is correct. >>> >>> I think most things are independent, with the exception of "shared vs exclusive >>> mappings", which I think becomes a dependency for a couple of things (marked in >>> depender description); again would be good to confirm. >>> >>> Finally, although I'm concentrating on the prerequisites to clear the path for >>> merging an MVP Large Anon Folios implementation, I've included one "enhancement" >>> item ("large folios in swap cache"), solely because we explicitly discussed it >>> last night. My view is that enhancements can come after the initial large anon >>> folios merge. Over time, I plan to add other enhancements (e.g. retain large >>> folios over COW, etc). >>> >>> I'm posting the table as yaml as that seemed easiest for email. You can convert >>> to csv with something like this in Python: >>> >>> import yaml >>> import pandas as pd >>> pd.DataFrame(yaml.safe_load(open('work-items.yml'))).to_csv('work-items.csv') >>> >>> Thanks, >>> Ryan >> Should we add the mremap case to the list? Like how to handle the case that mremap >> happens in the middle of large anonymous folio and fails to split it. > > What's the issue that you see here? My opinion is that if we do nothing special > for mremap(), it neither breaks correctness nor performance when we enable large > anon folios. So on that basis, its not a prerequisite and I'd rather leave it > off the list. We might want to do something later as an enhancement though? The issue is related with anonymous folio->index. If mremap happens in the middle of the large folio, current code doesn't split it. So the large folio will be split to two parts: one is in original place and another is in the new place. These two parts which are in different VMA have same folio->index. Can rmap_walk_anon() work with this situation? vma_address() combined with head page. Can it work for the pages not in same vma as head page? I could miss something here. Will try to build test against it. Regards Yin, Fengwei > > If we could always guarrantee that large anon folios were always naturally > aligned in VA space, then that would make many things simpler to implement. And > in that case, I can see the argument for doing something special in mremap(). > But since splitting a folio may fail, I guess we have to live with non-naturally > aligned folios for the general case, and therefore the simplification argument > goes out of the window? > > >