On Mon, Jan 12, 2026 at 12:15:54PM +0200, Mike Rapoport wrote: > > + * The tree is traversed using a key that encodes the page's physical > > address > > + * (pa) and its order into a single unsigned long value. The encoded key > > value > > + * is composed of two parts: the 'order bit' in the upper part and the > > 'page > > + * offset' in the lower part.:: > > + * > > + * > > +------------+-----------------------------+--------------------------+ > > + * | Page Order | Order Bit | Page Offset > > | > > + * > > +------------+-----------------------------+--------------------------+ > > + * | 0 | ...000100 ... (at bit 52) | pa >> (PAGE_SHIFT + 0) > > | > > + * | 1 | ...000010 ... (at bit 51) | pa >> (PAGE_SHIFT + 1) > > | > > + * | 2 | ...000001 ... (at bit 50) | pa >> (PAGE_SHIFT + 2) > > | > > + * | ... | ... | ... > > | > > + * > > +------------+-----------------------------+--------------------------+ > > + * > > + * Page Offset: > > To me "page offset" reads as offset from somewhere and here it's rather pfn > on steroids :) > Also in many places in the kernel "page offset" refers to the offset inside a > page. > > Can't say I can think of a better name, but it feels that it should express > that this is an address more explicitly.
It is "Shifted Physical Address" > > + node = phys_to_virt((phys_addr_t)node->table[idx]); > > + } > > + > > + /* Handle the leaf level bitmap (level 0) */ > > + leaf = (struct kho_radix_leaf *)node; > > + idx = kho_radix_get_index(key, 0); > > + __clear_bit(idx, leaf->bitmap); > > I think I already mentioned it in earlier reviews, but I don't remember any > response. > > How do we approach freeing empty bitmaps and intermediate nodes? > If we do a few preserve/uppreserve cycles for memory that can be allocated > and freed in between we might get many unused bitmaps. Surely this is an error case?? We shouldn't be unpreserving at all in a normal flow? > My view is that we should free the empty bitmaps, maybe asynchronously. > The intermediate nodes probably don't take that much memory to bother with > them. Telling they are empty would be quite expensive. I think we should not attempt to clean the tree unless there is a really good reason why we should have good flows with alot of unpreserving activity. I think we would be better served to treat the root cause and fixup what ever is doing preserving/unpreserving loops. Jason
