On Thu, Feb 18, 2016 at 10:20:24PM +0530, Aneesh Kumar K.V wrote: > Hello, > > This is a large series, mostly consisting of code movement. No new features > are done in this series. The changes are done to accomodate the upcoming new memory > model in future powerpc chips. The details of the new MMU model can be found at > > http://ibm.biz/power-isa3 (Needs registration). I am including a summary of the changes below. This doesn't apply against Linus' current tree - have you already posted the prerequisite patches? If so, what's the subject of the 0/N patch of the prerequisite series? > ISA 3.0 adds support for the radix tree style of MMU with full > virtualization and related control mechanisms that manage its > coexistence with the HPT. Radix-using operating systems will > manage their own translation tables instead of relying on hcalls. > > Radix style MMU model requires us to do a 4 level page table > with 64K and 4K page size. The table index size different page size > is listed below > > PGD -> 13 bits > PUD -> 9 (1G hugepage) > PMD -> 9 (2M huge page) > PTE -> 5 (for 64k), 9 (for 4k) > > We also require the page table to be in big endian format. > > The changes proposed in this series enables us to support both > hash page table and radix tree style MMU using a single kernel > with limited impact. The idea is to change core page table > accessors to static inline functions and later hotpatch them > to switch to hash or radix tree functions. For ex: > > static inline int pte_write(pte_t pte) > { > if (radix_enabled()) > return rpte_write(pte); > return hlpte_write(pte); > } Given that with a hash-based MMU, the Linux page tables are purely a software construct, I don't see why this complexity is necessary. We can make the PTE have the same format on radix and hash instead. I have a patch series that does that almost ready to post. > On boot we will hotpatch the code so as to avoid conditional operation. > > The other two major change propsed in this series is to switch hash > linux page table to a 4 level table in big endian format. This is > done so that functions like pte_val(), pud_populate() doesn't need > hotpatching and thereby helps in limiting runtime impact of the changes. Right, I agree with this. Paul. -- 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>