From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wei Wang Subject: Re: [PATCH v34 2/4] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT Date: Wed, 27 Jun 2018 11:00:05 +0800 Message-ID: <5B32FDB5.4040506@intel.com> References: <1529928312-30500-1-git-send-email-wei.w.wang@intel.com> <1529928312-30500-3-git-send-email-wei.w.wang@intel.com> <20180626002822-mutt-send-email-mst@kernel.org> <5B31B71B.6080709@intel.com> <20180626064338-mutt-send-email-mst@kernel.org> <5B323140.1000306@intel.com> <20180626163139-mutt-send-email-mst@kernel.org> <5B32E742.8080902@intel.com> <20180627053952-mutt-send-email-mst@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20180627053952-mutt-send-email-mst@kernel.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: "Michael S. Tsirkin" Cc: yang.zhang.wz@gmail.com, virtio-dev@lists.oasis-open.org, riel@redhat.com, quan.xu0@gmail.com, kvm@vger.kernel.org, nilal@redhat.com, liliang.opensource@gmail.com, linux-kernel@vger.kernel.org, mhocko@kernel.org, linux-mm@kvack.org, pbonzini@redhat.com, akpm@linux-foundation.org, virtualization@lists.linux-foundation.org, torvalds@linux-foundation.org List-Id: virtualization@lists.linuxfoundation.org On 06/27/2018 10:41 AM, Michael S. Tsirkin wrote: > On Wed, Jun 27, 2018 at 09:24:18AM +0800, Wei Wang wrote: >> On 06/26/2018 09:34 PM, Michael S. Tsirkin wrote: >>> On Tue, Jun 26, 2018 at 08:27:44PM +0800, Wei Wang wrote: >>>> On 06/26/2018 11:56 AM, Michael S. Tsirkin wrote: >>>>> On Tue, Jun 26, 2018 at 11:46:35AM +0800, Wei Wang wrote: >>>>> >>>>>>>> + if (!arrays) >>>>>>>> + return NULL; >>>>>>>> + >>>>>>>> + for (i = 0; i < max_array_num; i++) { >>>>>>> So we are getting a ton of memory here just to free it up a bit later. >>>>>>> Why doesn't get_from_free_page_list get the pages from free list for us? >>>>>>> We could also avoid the 1st allocation then - just build a list >>>>>>> of these. >>>>>> That wouldn't be a good choice for us. If we check how the regular >>>>>> allocation works, there are many many things we need to consider when pages >>>>>> are allocated to users. >>>>>> For example, we need to take care of the nr_free >>>>>> counter, we need to check the watermark and perform the related actions. >>>>>> Also the folks working on arch_alloc_page to monitor page allocation >>>>>> activities would get a surprise..if page allocation is allowed to work in >>>>>> this way. >>>>>> >>>>> mm/ code is well positioned to handle all this correctly. >>>> I'm afraid that would be a re-implementation of the alloc functions, >>> A re-factoring - you can share code. The main difference is locking. >>> >>>> and >>>> that would be much more complex than what we have. I think your idea of >>>> passing a list of pages is better. >>>> >>>> Best, >>>> Wei >>> How much memory is this allocating anyway? >>> >> For every 2TB memory that the guest has, we allocate 4MB. > Hmm I guess I'm missing something, I don't see it: > > > + max_entries = max_free_page_blocks(ARRAY_ALLOC_ORDER); > + entries_per_page = PAGE_SIZE / sizeof(__le64); > + entries_per_array = entries_per_page * (1 << ARRAY_ALLOC_ORDER); > + max_array_num = max_entries / entries_per_array + > + !!(max_entries % entries_per_array); > > Looks like you always allocate the max number? Yes. We allocated the max number and then free what's not used. For example, a 16TB guest, we allocate Four 4MB buffers and pass the 4 buffers to get_from_free_page_list. If it uses 3, then the remaining 1 "4MB buffer" will end up being freed. For today's guests, max_array_num is usually 1. Best, Wei