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
