On Thu, Mar 20 2025, Jason Gunthorpe wrote: >> I didn't mean the exact flags value, but the ability to have >> per-folio flags. The exact bits and their meaning would of course >> need to be part of the ABI. Shmem uses the dirty and uptodate flags >> to track some state on the folios, and the flags can affect it's >> behavior (lazily zeroing out falloc-ed pages for example). I am >> assuming other FD types or drivers might also want to store >> per-folio information. Having KHO core provide this facility can >> avoid duplicating the logic in each subsystem. > > For something simple like shmem I'd probably just suggest a side car bitmap > array or something? > > The trouble with trying to feed flags through the xarray thing is that > the memory holding that pfn data across the kexec is not itself > preserved memory so it is all blown away once the allocator starts. > > Any data that needs to be preserved further has to be copied into the > frozen struct page, which is pretty limiting in terms of what you > could preserve. A few bits could maybe work out but not alot of data.
Right, that makes sense. I can live with a sidecar bitmap then. [...] -- Regards, Pratyush Yadav
