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[79.181.91.42]) by smtp.gmail.com with ESMTPSA id v75sm24506057qka.38.2019.07.25.07.59.42 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Thu, 25 Jul 2019 07:59:47 -0700 (PDT) Date: Thu, 25 Jul 2019 10:59:40 -0400 From: "Michael S. Tsirkin" To: Alexander Duyck Cc: Nitesh Narayan Lal , Alexander Duyck , kvm@vger.kernel.org, david@redhat.com, dave.hansen@intel.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, yang.zhang.wz@gmail.com, pagupta@redhat.com, riel@surriel.com, konrad.wilk@oracle.com, lcapitulino@redhat.com, wei.w.wang@intel.com, aarcange@redhat.com, pbonzini@redhat.com, dan.j.williams@intel.com Subject: Re: [PATCH v2 5/5] virtio-balloon: Add support for providing page hints to host Message-ID: <20190725105852-mutt-send-email-mst@kernel.org> References: <20190724165158.6685.87228.stgit@localhost.localdomain> <20190724170514.6685.17161.stgit@localhost.localdomain> <20190724143902-mutt-send-email-mst@kernel.org> <21cc88cd-3577-e8b4-376f-26c7848f5764@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Thu, Jul 25, 2019 at 07:56:15AM -0700, Alexander Duyck wrote: > On Thu, 2019-07-25 at 10:44 -0400, Nitesh Narayan Lal wrote: > > On 7/24/19 3:02 PM, Michael S. Tsirkin wrote: > > > On Wed, Jul 24, 2019 at 10:05:14AM -0700, Alexander Duyck wrote: > > > > From: Alexander Duyck > > > > > > > > Add support for the page hinting feature provided by virtio-balloon. > > > > Hinting 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 respective > > > > free lists and are once again accessible by the guest system. > > > > > > > > Signed-off-by: Alexander Duyck > > > Looking at the design, it seems that hinted pages can immediately be > > > reused. I wonder how we can efficiently support this > > > with kvm when poisoning is in effect. Of course we can just > > > ignore the poison. However it seems cleaner to > > > 1. verify page is poisoned with the correct value > > > 2. fill the page with the correct value on fault > > > > > > Requirement 2 requires some kind of madvise that > > > will save the poison e.g. in the VMA. > > > > > > Not a blocker for sure ... > > > > > > > > > > --- > > > > drivers/virtio/Kconfig | 1 + > > > > drivers/virtio/virtio_balloon.c | 47 +++++++++++++++++++++++++++++++++++ > > > > include/uapi/linux/virtio_balloon.h | 1 + > > > > 3 files changed, 49 insertions(+) > > > > > > > > diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig > > > > index 078615cf2afc..d45556ae1f81 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_HINTING > > > > ---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_balloon.c > > > > index 226fbb995fb0..dee9f8f3ad09 100644 > > > > --- a/drivers/virtio/virtio_balloon.c > > > > +++ b/drivers/virtio/virtio_balloon.c > > > > @@ -19,6 +19,7 @@ > > > > #include > > > > #include > > > > #include > > > > +#include > > > > > > > > /* > > > > * Balloon device works in 4K page units. So each page is pointed to by > > > > @@ -27,6 +28,7 @@ > > > > */ > > > > #define VIRTIO_BALLOON_PAGES_PER_PAGE (unsigned)(PAGE_SIZE >> VIRTIO_BALLOON_PFN_SHIFT) > > > > #define VIRTIO_BALLOON_ARRAY_PFNS_MAX 256 > > > > +#define VIRTIO_BALLOON_ARRAY_HINTS_MAX 32 > > > > #define VIRTBALLOON_OOM_NOTIFY_PRIORITY 80 > > > > > > > > #define VIRTIO_BALLOON_FREE_PAGE_ALLOC_FLAG (__GFP_NORETRY | __GFP_NOWARN | \ > > > > @@ -46,6 +48,7 @@ enum virtio_balloon_vq { > > > > VIRTIO_BALLOON_VQ_DEFLATE, > > > > VIRTIO_BALLOON_VQ_STATS, > > > > VIRTIO_BALLOON_VQ_FREE_PAGE, > > > > + VIRTIO_BALLOON_VQ_HINTING, > > > > VIRTIO_BALLOON_VQ_MAX > > > > }; > > > > > > > > @@ -113,6 +116,10 @@ struct virtio_balloon { > > > > > > > > /* To register a shrinker to shrink memory upon memory pressure */ > > > > struct shrinker shrinker; > > > > + > > > > + /* Unused page hinting device */ > > > > + struct virtqueue *hinting_vq; > > > > + struct page_hinting_dev_info ph_dev_info; > > > > }; > > > > > > > > static struct virtio_device_id id_table[] = { > > > > @@ -152,6 +159,22 @@ static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq) > > > > > > > > } > > > > > > > > +void virtballoon_page_hinting_react(struct page_hinting_dev_info *ph_dev_info, > > > > + unsigned int num_hints) > > > > +{ > > > > + struct virtio_balloon *vb = > > > > + container_of(ph_dev_info, struct virtio_balloon, ph_dev_info); > > > > + struct virtqueue *vq = vb->hinting_vq; > > > > + unsigned int unused; > > > > + > > > > + /* We should always be able to add these buffers to an empty queue. */ > > > > > > can be an out of memory condition, and then ... > > > > Do we need an error check here? > > > > For situations where this fails we should disable hinting completely, maybe? > > No. Instead I will just limit the capacity to no more than the vq size. > Doing that should allow us to avoid the out of memory issue here if I am > understanding things correctly. > > I'm assuming the allocation being referred to is alloc_indirect_split(), > if so then it looks like it can fail and then we just fall back to using > the vring.desc directly which will work for my purposes as long as I limit > the capacity of the scatterlist to no more than the size of the vring. > Right. And maybe tweak the GFP mask - no reason to try to allocate memory aggressively with just 1 element in flight. >