On Thu, 11 Aug 2005, Gleb Natapov wrote: > What about the idea that was floating around about new VM flag that will > instruct kernel to copy pages belonging to the vma on fork instead of mark > them as cow?
It's a pretty good idea, and thanks for reminding us of it. It suffers from the general difficulty with fixes within get_user_pages, that we need down_write(&mm->mmap_sem) to split_vma, and even just to update vm_flags, whereas get_user_pages is entered with down_read. Really, we'd prefer not to mess with the vma itself in get_user_pages. Could mark the ptes instead, perhaps, but that gets very architecture- dependent. A separate array? not so nice if the vma is very large and the get_user_pages area very small. I had toyed with leaving the ptes in the parent as writable, made readonly just in the child; but though that violation could be excused while get_user_pages is active, it would have to be corrected at the end, and that gets complicated again. Hugh _______________________________________________ openib-general mailing list [email protected] http://openib.org/mailman/listinfo/openib-general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
