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Wed, 14 Aug 2019 11:47:53 +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 7F020600C8; Wed, 14 Aug 2019 11:47:41 +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> 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: <20190814122949.4946f438.cohuck@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable 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 [10.5.110.42]); Wed, 14 Aug 2019 11:47:53 +0000 (UTC) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 wit= h >> 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 >=3D (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= =2E >> >> 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_b= alloon.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 *v= b) >> +{ >> + struct device *dev =3D &vb->vdev->dev; >> + int err; >> + >> + vb->page_reporting_conf.report =3D virtballoon_report_pages; >> + vb->page_reporting_conf.max_pages =3D PAGE_REPORTING_MAX_PAGES; >> + err =3D page_reporting_enable(&vb->page_reporting_conf); >> + if (err < 0) { >> + dev_err(dev, "Failed to enable reporting, err =3D %d\n", err); >> + page_reporting_flag =3D false; > Should we clear the feature bit in this case as well? I think yes. If I am not wrong then in a case where page reporting setup fails for som= e 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. > >> + vb->page_reporting_conf.report =3D NULL; >> + vb->page_reporting_conf.max_pages =3D 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] =3D "deflate"; >> names[VIRTIO_BALLOON_VQ_STATS] =3D NULL; >> names[VIRTIO_BALLOON_VQ_FREE_PAGE] =3D NULL; >> + names[VIRTIO_BALLOON_VQ_REPORTING] =3D NULL; >> =20 >> if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) { >> names[VIRTIO_BALLOON_VQ_STATS] =3D "stats"; >> @@ -487,11 +536,18 @@ static int init_vqs(struct virtio_balloon *vb) >> callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] =3D NULL; >> } >> =20 >> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING)) { >> + names[VIRTIO_BALLOON_VQ_REPORTING] =3D "reporting_vq"; >> + callbacks[VIRTIO_BALLOON_VQ_REPORTING] =3D 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)). > >> + } >> err =3D vb->vdev->config->find_vqs(vb->vdev, VIRTIO_BALLOON_VQ_MAX, >> vqs, callbacks, names, NULL, NULL); >> if (err) >> return err; >> =20 >> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING)) >> + vb->reporting_vq =3D vqs[VIRTIO_BALLOON_VQ_REPORTING]; >> + >> vb->inflate_vq =3D vqs[VIRTIO_BALLOON_VQ_INFLATE]; >> vb->deflate_vq =3D 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 condit= ions to be true to enable page reporting. However, the order should be reversed because of the reason you mentioned= earlier. > >> virtio_device_ready(vdev); >> =20 >> if (towards_target(vb)) >> @@ -971,6 +1030,8 @@ static void virtballoon_remove(struct virtio_devi= ce *vdev) >> destroy_workqueue(vb->balloon_wq); >> } >> =20 >> + if (page_reporting_flag) >> + page_reporting_disable(&vb->page_reporting_conf); > I think you should not disable it if the feature bit was never offered > in the first place, right? Yes. I should check both feature bit and module parameter here. > >> remove_common(vb); >> #ifdef CONFIG_BALLOON_COMPACTION >> if (vb->vb_dev_info.inode) > (...) --=20 Thanks Nitesh