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nZyKcSKwuApcepJkm9W7oAdW02J4vbUEdSRXcoZLffcdm+m07wiTly3wD/VFw3aZdJ/R1MrE4aGl7xhnhjnYcyUWUoSxHDXTPsCKHzMQODtyPM4+CNQuQ6QERWAnPw5RC8vhRXRGTjj+J9R++24Djzn5IfR86Nj+Pcm5urMKpo454GaL2QHdAaA6ayVdROwSFmiDAEGs3SiAxvp9rkmZBBoOJUibN3ofskFSRAc7ix36CrPSyOqyrvR8yWq7GHSdaGvF/gcVn7FqIV7bDq5UqA945x7CmEZ/DbfewTuqup3p3AB6NapBHi5utAmQB5W0jGwDpK+tY7yIblKID9rc+q0Gss0OnUS156iTvGpb+MlV8ydbsARg9OmdMwDe8sQXv+hic/RSB7K0KzVg6Lo0tPOb5pUytyyeA3KbVvQU8xH+rIr0= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri Aug 7, 2026 at 5:22 PM EDT, Kairui Song wrote: > On Fri, Aug 07, 2026 at 10:18:05AM +0800, Zi Yan wrote: >> On Wed Aug 5, 2026 at 11:54 AM EDT, Kairui Song wrote: >> > On Wed, Aug 05, 2026 at 08:03:33AM +0800, Zi Yan wrote: >> >> On 5 Aug 2026, at 7:18, Shivam Kalra via B4 Relay wrote: >> >>=20 >> >> > Large shmem folios lose their address-space mapping when they are w= ritten >> >> > to swap, but remain valid members of the swap cache. Folios read fr= om swap >> >> > but not yet associated with an anon_vma can have the same mappingle= ss >> >> > swapcache state. folio_check_splittable() currently mistakes both c= ases for >> >> > truncation and rejects the split with -EBUSY. >> >> > >> >> > Implement the longstanding TODO for this state. Allow mappingless >> >> > swapcache folios to use the existing uniform order-0 swapcache spli= t path, >> >> > while continuing to reject truly truncated folios and unsupported >> >> > higher-order or non-uniform swapcache splits. >> >>=20 >> >> Thank you for your patches. >> >>=20 >> >> As Kairui (cc=E2=80=99d) mentioned in [1] (see =E2=80=9CA bit more de= tails on this=E2=80=9D), >> >> we might not need to implement this split. I will let Kairui to decid= e >> >> how we should deal with this patchset. >> >>=20 >> >> [1] https://lore.kernel.org/all/CAMgjq7CHDG8JhesSPMkn1kzG8jKb0BXO756B= vxMQC_MCn2eTyA@mail.gmail.com/ >> > >> > Thanks for the CC, this is actually not hard to implement as shown by >> > Shivam, I just found the code more and more hard to follow and fragile >> > as we add more logic to it. And we don't have to reject higher order >> > split either which can be seen easily if the code is cleaner. >> > >> > Personally I think doing some cleanup first is better, I haven't post = any >> > code as right now there doesn't seem to be much user of this. It will = be >> > needed if more clean THP swapcache begin to show up due to things like >> > THP readahead for swap, which isn't here yet. I think I can send an RF= C >> > tomorrow just for reference. I'm fine if we prefer to remove that TODO >> > using this smaller change first :) >>=20 >> Thanks. Can you also help review this patchset? The changes looks good >> to me but I am not sure if I get all the details about swapcache handlin= g. >>=20 >> --=20 >> Best Regards, >> Yan, Zi > > Hello, > > Thanks for the reminder, I got a bit busy so delayed for a day on that > RFC. > > For this series I think it's functionally fine, just the split logic is > a bit complex to follow and we still have restriction on swap cache > for order 0 uniform split only. I'll have a closer look later. Also I agree. I wonder if it is possible that a shmem in swapcache could enter non uniform split, folio_split(). With Patch 1, folio_check_splittable() will return -EINVAL, causing a WARN. Hi Shivam, Can you check the above issue? If it is possible, we want to avoid it. > let me know how you think about that RFC. Sure, will take a look. --=20 Best Regards, Yan, Zi