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[79.181.91.42]) by smtp.gmail.com with ESMTPSA id c5sm29604425qta.5.2019.07.24.13.46.05 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Wed, 24 Jul 2019 13:46:09 -0700 (PDT) Date: Wed, 24 Jul 2019 16:46:03 -0400 From: "Michael S. Tsirkin" To: Alexander Duyck Cc: Alexander Duyck , nitesh@redhat.com, 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 QEMU] virtio-balloon: Provide a interface for "bubble hinting" Message-ID: <20190724164433-mutt-send-email-mst@kernel.org> References: <20190724165158.6685.87228.stgit@localhost.localdomain> <20190724171050.7888.62199.stgit@localhost.localdomain> <20190724150224-mutt-send-email-mst@kernel.org> <6218af96d7d55935f2cf607d47680edc9b90816e.camel@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6218af96d7d55935f2cf607d47680edc9b90816e.camel@linux.intel.com> 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 Wed, Jul 24, 2019 at 01:18:00PM -0700, Alexander Duyck wrote: > On Wed, 2019-07-24 at 15:02 -0400, Michael S. Tsirkin wrote: > > On Wed, Jul 24, 2019 at 10:12:10AM -0700, Alexander Duyck wrote: > > > From: Alexander Duyck > > > > > > Add support for what I am referring to as "bubble hinting". Basically the > > > idea is to function very similar to how the balloon works in that we > > > basically end up madvising the page as not being used. However we don't > > > really need to bother with any deflate type logic since the page will be > > > faulted back into the guest when it is read or written to. > > > > > > This is meant to be a simplification of the existing balloon interface > > > to use for providing hints to what memory needs to be freed. I am assuming > > > this is safe to do as the deflate logic does not actually appear to do very > > > much other than tracking what subpages have been released and which ones > > > haven't. > > > > > > Signed-off-by: Alexander Duyck > > > --- > > > hw/virtio/virtio-balloon.c | 40 +++++++++++++++++++++++ > > > include/hw/virtio/virtio-balloon.h | 2 + > > > include/standard-headers/linux/virtio_balloon.h | 1 + > > > 3 files changed, 42 insertions(+), 1 deletion(-) > > > > > > diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c > > > index 2112874055fb..70c0004c0f88 100644 > > > --- a/hw/virtio/virtio-balloon.c > > > +++ b/hw/virtio/virtio-balloon.c > > > @@ -328,6 +328,39 @@ static void balloon_stats_set_poll_interval(Object *obj, Visitor *v, > > > balloon_stats_change_timer(s, 0); > > > } > > > > > > +static void virtio_bubble_handle_output(VirtIODevice *vdev, VirtQueue *vq) > > > +{ > > > + VirtQueueElement *elem; > > > + > > > + while ((elem = virtqueue_pop(vq, sizeof(VirtQueueElement)))) { > > > + unsigned int i; > > > + > > > + for (i = 0; i < elem->in_num; i++) { > > > + void *addr = elem->in_sg[i].iov_base; > > > + size_t size = elem->in_sg[i].iov_len; > > > + ram_addr_t ram_offset; > > > + size_t rb_page_size; > > > + RAMBlock *rb; > > > + > > > + if (qemu_balloon_is_inhibited()) > > > + continue; > > > + > > > + rb = qemu_ram_block_from_host(addr, false, &ram_offset); > > > + rb_page_size = qemu_ram_pagesize(rb); > > > + > > > + /* For now we will simply ignore unaligned memory regions */ > > > + if ((ram_offset | size) & (rb_page_size - 1)) > > > + continue; > > > + > > > + ram_block_discard_range(rb, ram_offset, size); > > > > I suspect this needs to do like the migration type of > > hinting and get disabled if page poisoning is in effect. > > Right? > > Shouldn't something like that end up getting handled via > qemu_balloon_is_inhibited, or did I miss something there? I assumed cases > like that would end up setting qemu_balloon_is_inhibited to true, if that > isn't the case then I could add some additional conditions. I would do it > in about the same spot as the qemu_balloon_is_inhibited check. Well qemu_balloon_is_inhibited is for the regular ballooning, mostly a work-around for limitations is host linux iommu APIs when it's used with VFIO. -- MST