Ram Pai <linux...@us.ibm.com> writes: > Rearrange PTE bits to free up bits 3, 4, 5 and 6 for > memory keys. Bit 3, 4, 5, 6 and 57 shall be used for memory > keys. > > The patch does the following change to the 64K PTE format > > H_PAGE_BUSY moves from bit 3 to bit 7 > H_PAGE_F_SECOND which occupied bit 4 moves to the second part > of the pte. > H_PAGE_F_GIX which occupied bit 5, 6 and 7 also moves to the > second part of the pte. > > The second part of the PTE will hold > a (H_PAGE_F_SECOND|H_PAGE_F_GIX) for 64K page backed pte, > and sixteen (H_PAGE_F_SECOND|H_PAGE_F_GIX) for 4k backed > pte. > > the four bits((H_PAGE_F_SECOND|H_PAGE_F_GIX) that represent a slot > is initialized to 0xF indicating a invalid slot. if a hashpage does > get allocated to the 0xF slot, it is released and not used. In > other words, even though 0xF is a valid slot we discard it and > consider it as invalid slot(HPTE_SOFT_INVALID). This gives us an > opportunity to not depend on a bit in the primary PTE in order to > determine the validity of a slot. > > When we release a 0xF slot we also release a legitimate primary > slot and unmap that entry. This is to ensure that we do get > a legimate non-0xF slot the next time we retry for a slot. > > Though treating 0xF slot as invalid reduces the number of available > slots and make have a effect on the performance, the probabilty > of hitting a 0xF is extermely low. > > Compared to the current scheme, the above described scheme reduces > the number of false hash table updates significantly and has the > added advantage of releasing four valuable PTE bits for other > purpose. > > This idea was jointly developed by Paul Mackerras, Aneesh, Michael > Ellermen and myself. > > 4K PTE format remain unchanged currently. >
Can you also split this patch into two. One which changes __hash_page_4k() ie, linux pte format w.r.t 4k hash pte. Second patch with changes w.r.t __hash_page_64k() ie, pte format w.r.t 64k hash pte. -aneesh