From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2E045C433FF for ; Wed, 14 Aug 2019 14:01:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E6ADC2064A for ; Wed, 14 Aug 2019 14:01:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728036AbfHNOBv convert rfc822-to-8bit (ORCPT ); Wed, 14 Aug 2019 10:01:51 -0400 Received: from mx1.redhat.com ([209.132.183.28]:24083 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726525AbfHNOBu (ORCPT ); Wed, 14 Aug 2019 10:01:50 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 872DE3175299; Wed, 14 Aug 2019 14:01:49 +0000 (UTC) Received: from [10.18.17.163] (dhcp-17-163.bos.redhat.com [10.18.17.163]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 957748063A; Wed, 14 Aug 2019 14:01:39 +0000 (UTC) Subject: Re: [RFC][Patch v12 2/2] virtio-balloon: interface to support free page reporting To: Cornelia Huck Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, virtio-dev@lists.oasis-open.org, pbonzini@redhat.com, lcapitulino@redhat.com, pagupta@redhat.com, wei.w.wang@intel.com, yang.zhang.wz@gmail.com, riel@surriel.com, david@redhat.com, mst@redhat.com, dodgen@google.com, konrad.wilk@oracle.com, dhildenb@redhat.com, aarcange@redhat.com, alexander.duyck@gmail.com, john.starks@microsoft.com, dave.hansen@intel.com, mhocko@suse.com References: <20190812131235.27244-1-nitesh@redhat.com> <20190812131235.27244-3-nitesh@redhat.com> <20190814122949.4946f438.cohuck@redhat.com> <20190814154217.4a4e2ee1.cohuck@redhat.com> From: Nitesh Narayan Lal Openpgp: preference=signencrypt Autocrypt: addr=nitesh@redhat.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190814154217.4a4e2ee1.cohuck@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.49]); Wed, 14 Aug 2019 14:01:49 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/14/19 9:42 AM, Cornelia Huck wrote: > On Wed, 14 Aug 2019 07:47:40 -0400 > Nitesh Narayan Lal wrote: > >> On 8/14/19 6:29 AM, Cornelia Huck wrote: >>> On Mon, 12 Aug 2019 09:12:35 -0400 >>> Nitesh Narayan Lal wrote: >>> >>>> Enables the kernel to negotiate VIRTIO_BALLOON_F_REPORTING feature with >>>> the host. If it is available and page_reporting_flag is set to true, >>>> page_reporting is enabled and its callback is configured along with >>>> the max_pages count which indicates the maximum number of pages that >>>> can be isolated and reported at a time. Currently, only free pages of >>>> order >= (MAX_ORDER - 2) are reported. To prevent any false OOM >>>> max_pages count is set to 16. >>>> >>>> By default page_reporting feature is enabled and gets loaded as soon >>>> as the virtio-balloon driver is loaded. However, it could be disabled >>>> by writing the page_reporting_flag which is a virtio-balloon parameter. >>>> >>>> Signed-off-by: Nitesh Narayan Lal >>>> --- >>>> drivers/virtio/Kconfig | 1 + >>>> drivers/virtio/virtio_balloon.c | 64 ++++++++++++++++++++++++++++- >>>> include/uapi/linux/virtio_balloon.h | 1 + >>>> 3 files changed, 65 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c >>>> index 226fbb995fb0..defec00d4ee2 100644 >>>> --- a/drivers/virtio/virtio_balloon.c >>>> +++ b/drivers/virtio/virtio_balloon.c >>> (...) >>> >>>> +static void virtballoon_page_reporting_setup(struct virtio_balloon *vb) >>>> +{ >>>> + struct device *dev = &vb->vdev->dev; >>>> + int err; >>>> + >>>> + vb->page_reporting_conf.report = virtballoon_report_pages; >>>> + vb->page_reporting_conf.max_pages = PAGE_REPORTING_MAX_PAGES; >>>> + err = page_reporting_enable(&vb->page_reporting_conf); >>>> + if (err < 0) { >>>> + dev_err(dev, "Failed to enable reporting, err = %d\n", err); >>>> + page_reporting_flag = false; >>> Should we clear the feature bit in this case as well? >> I think yes. > Eww, I didn't recall that we don't call the ->probe callback until > after feature negotiation has finished, so scratch that particular idea. > > For what reasons may page_reporting_enable() fail? If the guest is low in memory and some allocation required for page reporting setup fails. > Does it make sense > to fail probing the device in that case? And does it make sense to > re-try later (i.e. leave page_reporting_flag set)? Re-trying to setup page reporting will mean that virtballoon_probe has to be called again. For which the driver has to be re-loaded, isn't? > >> If I am not wrong then in a case where page reporting setup fails for some >> reason and at a later point the user wants to re-enable it then for that balloon >> driver has to be reloaded. >> Which would mean re-negotiation of the feature bit. > Re-negotiation actually already happens if a driver is unbound and > rebound. > >>> >>>> + vb->page_reporting_conf.report = NULL; >>>> + vb->page_reporting_conf.max_pages = 0; >>>> + return; >>>> + } >>>> +} >>>> + >>>> static void set_page_pfns(struct virtio_balloon *vb, >>>> __virtio32 pfns[], struct page *page) >>>> { >>>> @@ -476,6 +524,7 @@ static int init_vqs(struct virtio_balloon *vb) >>>> names[VIRTIO_BALLOON_VQ_DEFLATE] = "deflate"; >>>> names[VIRTIO_BALLOON_VQ_STATS] = NULL; >>>> names[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL; >>>> + names[VIRTIO_BALLOON_VQ_REPORTING] = NULL; >>>> >>>> if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) { >>>> names[VIRTIO_BALLOON_VQ_STATS] = "stats"; >>>> @@ -487,11 +536,18 @@ static int init_vqs(struct virtio_balloon *vb) >>>> callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL; >>>> } >>>> >>>> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING)) { >>>> + names[VIRTIO_BALLOON_VQ_REPORTING] = "reporting_vq"; >>>> + callbacks[VIRTIO_BALLOON_VQ_REPORTING] = balloon_ack; >>> Do we even want to try to set up the reporting queue if reporting has >>> been disabled via module parameter? Might make more sense to not even >>> negotiate the feature bit in that case. >> True. >> I think this should be replaced with something like (page_reporting_flag && >> virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING)). > Yes. > > Is page_reporting_flag supposed to be changeable on the fly? Yes. > The only > way to really turn off the feature bit from the driver is to not pass > in the feature in the features table; we could provide two different > tables depending on the flag if it were static. I did have a plan of moving to static keys eventually instead of using module parameters for this purpose. :) That way I will be able to just control the kernel side of things on the fly without changing the balloon-page-reporting framework. The objective is to allow the user to enable/disable page tracking on the fly. > >>> >>>> + } >>>> err = vb->vdev->config->find_vqs(vb->vdev, VIRTIO_BALLOON_VQ_MAX, >>>> vqs, callbacks, names, NULL, NULL); >>>> if (err) >>>> return err; >>>> >>>> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING)) >>>> + vb->reporting_vq = vqs[VIRTIO_BALLOON_VQ_REPORTING]; >>>> + >>>> vb->inflate_vq = vqs[VIRTIO_BALLOON_VQ_INFLATE]; >>>> vb->deflate_vq = vqs[VIRTIO_BALLOON_VQ_DEFLATE]; >>>> if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) { >>>> @@ -924,6 +980,9 @@ static int virtballoon_probe(struct virtio_device *vdev) >>>> if (err) >>>> goto out_del_balloon_wq; >>>> } >>>> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING) && >>>> + page_reporting_flag) >>>> + virtballoon_page_reporting_setup(vb); >>> In that case, you'd only need to check for the feature bit here. >> Why is that? >> I think both the checks should be present here as we need both the conditions to >> be true to enable page reporting. > Yeah, because we can't clear the feature bit if the flag is not set. +1 > >> However, the order should be reversed because of the reason you mentioned earlier. >> >>> >>>> virtio_device_ready(vdev); >>>> >>>> if (towards_target(vb)) -- Thanks Nitesh