On Tue, 2014-05-06 at 21:38 +0530, Aneesh Kumar K.V wrote: > >> I updated the commit message as below. Let me know if this is ok. > >> > >> KVM: PPC: BOOK3S: HV: THP support for guest > > > > This has nothing to do with THP. > > THP support in guest depend on KVM advertising MPSS feature. We already > have rest of the changes needed to support transparent huge pages > upstream. (We do support THP with PowerVM LPAR already). The primary > motivation of this patch is to enable THP in powerkvm guest. I would argue (nit picking, I know ... :-) that the subject should be "Enable MPSS support for guests", and the description can then explain that this allows Linux guests to use THP. Cheers, Ben. > > > >> > >> On recent IBM Power CPUs, while the hashed page table is looked up using > >> the page size from the segmentation hardware (i.e. the SLB), it is > >> possible to have the HPT entry indicate a larger page size. Thus for > >> example it is possible to put a 16MB page in a 64kB segment, but since > >> the hash lookup is done using a 64kB page size, it may be necessary to > >> put multiple entries in the HPT for a single 16MB page. This > >> capability is called mixed page-size segment (MPSS). With MPSS, > >> there are two relevant page sizes: the base page size, which is the > >> size used in searching the HPT, and the actual page size, which is the > >> size indicated in the HPT entry. [ Note that the actual page size is > >> always >= base page size ]. > >> > >> We advertise MPSS feature to guest only if the host CPU supports the > >> same. We use "ibm,segment-page-sizes" device tree node to advertise > >> the MPSS support. The penc encoding indicate whether we support > >> a specific combination of base page size and actual page size > >> in the same segment. It is also the value used in the L|LP encoding > >> of HPTE entry. > >> > >> In-order to support MPSS in guest, KVM need to handle the below details > >> * advertise MPSS via ibm,segment-page-sizes > >> * Decode the base and actual page size correctly from the HPTE entry > >> so that we know what we are dealing with in H_ENTER and and can do > > > > Which code path exactly changes for H_ENTER? > > There is no real code path changes. Any code path that use > hpte_page_size() is impacted. We return actual page size there. > > > > >> the appropriate TLB invalidation in H_REMOVE and evictions. > > > > Apart from the grammar (which is pretty broken for the part that is not > > copied from Paul) and the subject line this sounds quite reasonable. > > > > Wll try to fix. > > -aneesh -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
