Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > Why do we want to track that information on a per-page basis? Wouldn't it > be easier to have a VM_NOCOW flag in vma->vm_flags? Set it the first > time somebody does an O_DIRECT read or RDMA pin. That's it. Pages in > that VMA will now never be COWed, regardless of their refcount/mapcount. > And the whole "did we pin or get this page" problem goes away. Along > with folio->pincount. Wouldn't that potentially make someone's entire malloc() heap entirely NOCOW if they did a single DIO to/from it. Also you only mention DIO read - but what about "start DIO write; fork(); touch buffer" in the parent - now the write buffer belongs to the child and they can affect the parent's write. David
