From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Aneesh Kumar K.V" Subject: Re: [RFC PATCH] KVM: PPC: BOOK3S: HV: THP support for guest Date: Tue, 06 May 2014 19:55:34 +0530 Message-ID: <87r447q90h.fsf@linux.vnet.ibm.com> References: <1399224616-25142-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <53677834.5010808@suse.de> <87lhug9taz.fsf@linux.vnet.ibm.com> <20140506042058.GA25186@drongo> Mime-Version: 1.0 Content-Type: text/plain Cc: Alexander Graf , benh@kernel.crashing.org, linuxppc-dev@lists.ozlabs.org, kvm-ppc@vger.kernel.org, kvm@vger.kernel.org To: Paul Mackerras Return-path: In-Reply-To: <20140506042058.GA25186@drongo> Sender: kvm-ppc-owner@vger.kernel.org List-Id: kvm.vger.kernel.org Paul Mackerras writes: > On Mon, May 05, 2014 at 08:17:00PM +0530, Aneesh Kumar K.V wrote: >> Alexander Graf writes: >> >> > On 05/04/2014 07:30 PM, Aneesh Kumar K.V wrote: >> >> Signed-off-by: Aneesh Kumar K.V >> > >> > No patch description, no proper explanations anywhere why you're doing >> > what. All of that in a pretty sensitive piece of code. There's no way >> > this patch can go upstream in its current form. >> > >> >> Sorry about being vague. Will add a better commit message. The goal is >> to export MPSS support to guest if the host support the same. MPSS >> support is exported via penc encoding in "ibm,segment-page-sizes". The >> actual format can be found at htab_dt_scan_page_sizes. When the guest >> memory is backed by hugetlbfs we expose the penc encoding the host >> support to guest via kvmppc_add_seg_page_size. > > In a case like this it's good to assume the reader doesn't know very > much about Power CPUs, and probably isn't familiar with acronyms such > as MPSS. The patch needs an introductory paragraph explaining that 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. I will update the commit message with the above details -aneesh