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nnjfK7pNKUDSKMjVI2oZ/wljVdxKcb4l7cZdX66e9JSma2TR9+Z+lQb/z3YJII8MS/JJtcKJBcRIoT975/cvZZLTQOCVw0Npef2epoO2/qB7gJ2tFLyZ6SIM9hobEVR9g/jyi+VRn29wBAJgqNW/UEm6tPyYibDCqNby3EV4+NV0xUTS7VYyKhMRbQMcv3iR9fgLIHDM6laRGQ9/uEUe8WyKDzeHG9D05285bUidiTEx9X7z+KBVy2W7JQS11LC8Fib/QNNCFuNQGpeF5DPUxP+VBIMfH8cKBfWxhT+/2m0L/qFTX48ZDUlTsMbNffWKCUQ1I X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 8/30/2023 6:08 PM, Ryan Roberts wrote: > On 24/07/2023 10:33, Yin, Fengwei wrote: >> >> >> 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. > > Hi Fengwei, > > Did you ever reach a conclusion on this? Based on David's comment, I'm assuming > this is not a problem and already handled correctly for pte-mapped THP? Yes. It's not a real problem. > > I guess vma->vm_pgoff is fixed up in the new vma representing the remapped > portion to take account of the offset? (just a guess). Yes. vma->vm_pgoff keep unchanged for mremap target vma. So the rmap walk can walk the source vma and target vma. Regards Yin, Fengwei > > Thanks, > Ryan > > >> >> >> 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? >>> >>> >>> >