On 07/25/2013 08:26 PM, Alexey Kardashevskiy wrote: > The current VFIO-on-POWER implementation supports only user mode > driven mapping, i.e. QEMU is sending requests to map/unmap pages. > However this approach is really slow, so we want to move that to KVM. > Since H_PUT_TCE can be extremely performance sensitive (especially with > network adapters where each packet needs to be mapped/unmapped) we chose > to implement that as a "fast" hypercall directly in "real > mode" (processor still in the guest context but MMU off). > > To be able to do that, we need to provide some facilities to > access the struct page count within that real mode environment as things > like the sparsemem vmemmap mappings aren't accessible. > > This adds an API to get page struct when MMU is off. > > This adds to MM a new function put_page_unless_one() which drops a page > if counter is bigger than 1. It is going to be used when MMU is off > (real mode on PPC64 is the first user) and we want to make sure that page > release will not happen in real mode as it may crash the kernel in > a horrible way. Yes, my english needs to be polished, I even know where :) -- Alexey -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>