From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wei Wang Subject: Re: [PATCH v12 6/8] mm: support reporting free page blocks Date: Wed, 26 Jul 2017 10:22:23 +0800 Message-ID: <5977FCDF.7040606@intel.com> References: <20170717152448.GN12888@dhcp22.suse.cz> <596D6E7E.4070700@intel.com> <20170719081311.GC26779@dhcp22.suse.cz> <596F4A0E.4010507@intel.com> <20170724090042.GF25221@dhcp22.suse.cz> <59771010.6080108@intel.com> <20170725112513.GD26723@dhcp22.suse.cz> <597731E8.9040803@intel.com> <20170725124141.GF26723@dhcp22.suse.cz> <286AC319A985734F985F78AFA26841F739283F62@shsmsx102.ccr.corp.intel.com> <20170725145333.GK26723@dhcp22.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Cc: "Michael S. Tsirkin" , "linux-kernel@vger.kernel.org" , "qemu-devel@nongnu.org" , "virtualization@lists.linux-foundation.org" , "kvm@vger.kernel.org" , "linux-mm@kvack.org" , "david@redhat.com" , "cornelia.huck@de.ibm.com" , "akpm@linux-foundation.org" , "mgorman@techsingularity.net" , "aarcange@redhat.com" , "amit.shah@redhat.com" , "pbonzini@redhat.com" , "liliang.opensource@gmail.com" , "virtio-dev@lists.oasis-open.org" , "yang.zhang.wz@gmail.com" , "quan.xu@a To: Michal Hocko Return-path: Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: In-Reply-To: <20170725145333.GK26723@dhcp22.suse.cz> List-Id: kvm.vger.kernel.org On 07/25/2017 10:53 PM, Michal Hocko wrote: > On Tue 25-07-17 14:47:16, Wang, Wei W wrote: >> On Tuesday, July 25, 2017 8:42 PM, hal Hocko wrote: >>> On Tue 25-07-17 19:56:24, Wei Wang wrote: >>>> On 07/25/2017 07:25 PM, Michal Hocko wrote: >>>>> On Tue 25-07-17 17:32:00, Wei Wang wrote: >>>>>> On 07/24/2017 05:00 PM, Michal Hocko wrote: >>>>>>> On Wed 19-07-17 20:01:18, Wei Wang wrote: >>>>>>>> On 07/19/2017 04:13 PM, Michal Hocko wrote: >>>>>>> [... >>>> We don't need to do the pfn walk in the guest kernel. When the API >>>> reports, for example, a 2MB free page block, the API caller offers to >>>> the hypervisor the base address of the page block, and size=2MB, to >>>> the hypervisor. >>> So you want to skip pfn walks by regularly calling into the page allocator to >>> update your bitmap. If that is the case then would an API that would allow you >>> to update your bitmap via a callback be s sufficient? Something like >>> void walk_free_mem(int node, int min_order, >>> void (*visit)(unsigned long pfn, unsigned long nr_pages)) >>> >>> The function will call the given callback for each free memory block on the given >>> node starting from the given min_order. The callback will be strictly an atomic >>> and very light context. You can update your bitmap from there. >> I would need to introduce more about the background here: >> The hypervisor and the guest live in their own address space. The hypervisor's bitmap >> isn't seen by the guest. I think we also wouldn't be able to give a callback function >> from the hypervisor to the guest in this case. > How did you plan to use your original API which export struct page array > then? That's where the virtio-balloon driver comes in. It uses a shared ring mechanism to send the guest memory info to the hypervisor. We didn't expose the struct page array from the guest to the hypervisor. For example, when a 2MB free page block is reported from the free page list, the info put on the ring is just (base address of the 2MB continuous memory, size=2M). > >>> This would address my main concern that the allocator internals would get >>> outside of the allocator proper. >> What issue would it have to expose the internal, for_each_zone()? > zone is a MM internal concept. No code outside of the MM proper should > really care about zones. I think this is also what Andrew suggested in the previous discussion: https://lkml.org/lkml/2017/3/16/951 Move the code to virtio-balloon and a little layering violation seems acceptable. Best, Wei