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: > >> > >> > Large shmem folios lose their address-space mapping when they are written > >> > to swap, but remain valid members of the swap cache. Folios read from > >> > swap > >> > but not yet associated with an anon_vma can have the same mappingless > >> > swapcache state. folio_check_splittable() currently mistakes both cases > >> > 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 split > >> > path, > >> > while continuing to reject truly truncated folios and unsupported > >> > higher-order or non-uniform swapcache splits. > >> > >> Thank you for your patches. > >> > >> As Kairui (cc’d) mentioned in [1] (see “A bit more details on this”), > >> we might not need to implement this split. I will let Kairui to decide > >> how we should deal with this patchset. > >> > >> [1] > >> https://lore.kernel.org/all/camgjq7chdg8jhesspmkn1kzg8jkb0bxo756bvxmqc_mcn2e...@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 RFC > > tomorrow just for reference. I'm fine if we prefer to remove that TODO > > using this smaller change first :) > > 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 handling. > > -- > 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 let me know how you think about that RFC.
