Dave Hansen wrote: > Well, and more fundamentally: do we really want dup_mm() able to be > called from other code? > > Maybe we need a bit more detailed justification why fork() itself isn't > good enough. It looks to me like they basically need an arch-specific > argument to fork, telling the new process's page tables to take the > fancy new bit. > > I'm really curious how this new stuff is going to get used. Are you > basically replacing fork() when creating kvm guests? No. The trick is, that we do need bigger page tables when running guests: our page tables are usually 2k, but when running a guest they're 4k to track both guest and host dirty&reference information. This looks like this: *----------* *2k PTE's * *----------* *2k PGSTE * *----------* We don't want to waste precious memory for all page tables. We'd like to have one kernel image that runs regular server workload _and_ guests. Therefore, we need to reallocate the page table after fork() once we know that task is going to be a hypervisor. That's what this code does: reallocate a bigger page table to accomondate the extra information. The task needs to be single-threaded when calling for extended page tables. Btw: at fork() time, we cannot tell whether or not the user's going to be a hypervisor. Therefore we cannot do this in fork. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/virtualization
