On 01.02.22 16:48, Alex Sierra wrote: > Device memory that is cache coherent from device and CPU point of view. > This is used on platforms that have an advanced system bus (like CAPI > or CXL). Any page of a process can be migrated to such memory. However, > no one should be allowed to pin such memory so that it can always be > evicted. > > Signed-off-by: Alex Sierra <alex.sierra@xxxxxxx> > Acked-by: Felix Kuehling <Felix.Kuehling@xxxxxxx> > Reviewed-by: Alistair Popple <apopple@xxxxxxxxxx> So, I'm currently messing with PageAnon() pages and CoW semantics ... all these PageAnon() ZONE_DEVICE variants don't necessarily make my life easier but I'm not sure yet if they make my life harder. I hope you can help me understand some of that stuff. 1) What are expected CoW semantics for DEVICE_COHERENT? I assume we'll share them just like other PageAnon() pages during fork() readable, and the first sharer writing to them receives an "ordinary" !ZONE_DEVICE copy. So this would be just like DEVICE_EXCLUSIVE CoW handling I assume, just that we don't have to go through the loop of restoring a device exclusive entry? 2) How are these pages freed to clear/invalidate PageAnon() ? I assume for PageAnon() ZONE_DEVICE pages we'll always for via free_devmap_managed_page(), correct? 3) FOLL_PIN While you write "no one should be allowed to pin such memory", patch #2 only blocks FOLL_LONGTERM. So I assume we allow ordinary FOLL_PIN and you might want to be a bit more precise? ... I'm pretty sure we cannot FOLL_PIN DEVICE_PRIVATE pages, but can we FILL_PIN DEVICE_EXCLUSIVE pages? I strongly assume so? Thanks for any information. -- Thanks, David / dhildenb
