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Tue, 11 Feb 2020 11:04:13 +0000 (UTC) Received: from [10.36.117.14] (ovpn-117-14.ams2.redhat.com [10.36.117.14]) by smtp.corp.redhat.com (Postfix) with ESMTP id E6A815C1B2; Tue, 11 Feb 2020 11:03:57 +0000 (UTC) Subject: Re: [PATCH v16.1 6/9] virtio-balloon: Add support for providing free page reports to host To: Alexander Duyck , kvm@vger.kernel.org, mst@redhat.com, linux-kernel@vger.kernel.org, willy@infradead.org, mhocko@kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, mgorman@techsingularity.net, vbabka@suse.cz Cc: yang.zhang.wz@gmail.com, nitesh@redhat.com, konrad.wilk@oracle.com, pagupta@redhat.com, riel@surriel.com, lcapitulino@redhat.com, dave.hansen@intel.com, wei.w.wang@intel.com, aarcange@redhat.com, pbonzini@redhat.com, dan.j.williams@intel.com, alexander.h.duyck@linux.intel.com, osalvador@suse.de References: <20200122173040.6142.39116.stgit@localhost.localdomain> <20200122174347.6142.92803.stgit@localhost.localdomain> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <20200122174347.6142.92803.stgit@localhost.localdomain> Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Content-Transfer-Encoding: quoted-printable 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 22.01.20 18:43, Alexander Duyck wrote: > From: Alexander Duyck >=20 > Add support for the page reporting feature provided by virtio-balloon. > Reporting differs from the regular balloon functionality in that is is > much less durable than a standard memory balloon. Instead of creating a > list of pages that cannot be accessed the pages are only inaccessible > while they are being indicated to the virtio interface. Once the > interface has acknowledged them they are placed back into their respect= ive > free lists and are once again accessible by the guest system. >=20 > Unlike a standard balloon we don't inflate and deflate the pages. Inste= ad > we perform the reporting, and once the reporting is completed it is > assumed that the page has been dropped from the guest and will be fault= ed > back in the next time the page is accessed. >=20 > Acked-by: Michael S. Tsirkin > Reviewed-by: David Hildenbrand > Signed-off-by: Alexander Duyck > --- > drivers/virtio/Kconfig | 1 + > drivers/virtio/virtio_balloon.c | 64 +++++++++++++++++++++++++++= ++++++++ > include/uapi/linux/virtio_balloon.h | 1 + > 3 files changed, 66 insertions(+) >=20 > diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig > index 078615cf2afc..4b2dd8259ff5 100644 > --- a/drivers/virtio/Kconfig > +++ b/drivers/virtio/Kconfig > @@ -58,6 +58,7 @@ config VIRTIO_BALLOON > tristate "Virtio balloon driver" > depends on VIRTIO > select MEMORY_BALLOON > + select PAGE_REPORTING > ---help--- > This driver supports increasing and decreasing the amount > of memory within a KVM guest. > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_ba= lloon.c > index 40bb7693e3de..a07b9e18a292 100644 > --- a/drivers/virtio/virtio_balloon.c > +++ b/drivers/virtio/virtio_balloon.c > @@ -19,6 +19,7 @@ > #include > #include > #include > +#include > =20 > /* > * Balloon device works in 4K page units. So each page is pointed to = by > @@ -47,6 +48,7 @@ enum virtio_balloon_vq { > VIRTIO_BALLOON_VQ_DEFLATE, > VIRTIO_BALLOON_VQ_STATS, > VIRTIO_BALLOON_VQ_FREE_PAGE, > + VIRTIO_BALLOON_VQ_REPORTING, > VIRTIO_BALLOON_VQ_MAX > }; > =20 > @@ -114,6 +116,10 @@ struct virtio_balloon { > =20 > /* To register a shrinker to shrink memory upon memory pressure */ > struct shrinker shrinker; > + > + /* Free page reporting device */ > + struct virtqueue *reporting_vq; > + struct page_reporting_dev_info pr_dev_info; > }; > =20 > static struct virtio_device_id id_table[] =3D { > @@ -153,6 +159,33 @@ static void tell_host(struct virtio_balloon *vb, s= truct virtqueue *vq) > =20 > } > =20 > +int virtballoon_free_page_report(struct page_reporting_dev_info *pr_de= v_info, > + struct scatterlist *sg, unsigned int nents) > +{ > + struct virtio_balloon *vb =3D > + container_of(pr_dev_info, struct virtio_balloon, pr_dev_info); > + struct virtqueue *vq =3D vb->reporting_vq; > + unsigned int unused, err; > + > + /* We should always be able to add these buffers to an empty queue. *= / > + err =3D virtqueue_add_inbuf(vq, sg, nents, vb, GFP_NOWAIT | __GFP_NOW= ARN); > + > + /* > + * In the extremely unlikely case that something has occurred and we > + * are able to trigger an error we will simply display a warning > + * and exit without actually processing the pages. > + */ > + if (WARN_ON_ONCE(err)) > + return err; > + > + virtqueue_kick(vq); > + > + /* When host has read buffer, this completes via balloon_ack */ > + wait_event(vb->acked, virtqueue_get_buf(vq, &unused)); > + > + return 0; > +} Did you see the discussion regarding unifying handling of inflate/deflate/free_page_hinting_free_page_reporting, requested by Michael? I think free page reporting is special and shall be left alone. VIRTIO_BALLOON_F_REPORTING is nothing but a more advanced inflate, right (sg, inflate based on size - not "virtio pages")? And you rely on deflates not being required before reusing an inflated page. I suggest the following: /* New interface (+ 2 virtqueues) to inflate/deflate using a SG */ VIRTIO_BALLOON_F_SG /* * No need to deflate when reusing pages (once the inflate request was * processed). Applies to all inflate queues. */ VIRTIO_BALLOON_F_OPTIONAL_DEFLATE And two new virtqueues VIRTIO_BALLOON_VQ_INFLATE_SG VIRTIO_BALLOON_VQ_DEFLATE_SG Your feature would depend on VIRTIO_BALLOON_F_SG && VIRTIO_BALLOON_F_OPTIONAL_DEFLATE. VIRTIO_BALLOON_F_OPTIONAL_DEFLATE could be reused to avoid deflating on certain events (e.g., from OOM/shrinker). Thoughts? --=20 Thanks, David / dhildenb