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[192.55.52.120]) by mx.google.com with ESMTPS id c38si6039390pgc.65.2019.07.24.14.14.43 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 24 Jul 2019 14:14:44 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of alexander.h.duyck@linux.intel.com designates 192.55.52.120 as permitted sender) client-ip=192.55.52.120; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of alexander.h.duyck@linux.intel.com designates 192.55.52.120 as permitted sender) smtp.mailfrom=alexander.h.duyck@linux.intel.com; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=intel.com X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga001.jf.intel.com ([10.7.209.18]) by fmsmga104.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 24 Jul 2019 14:14:43 -0700 X-IronPort-AV: E=Sophos;i="5.64,304,1559545200"; d="scan'208";a="253724062" Received: from ahduyck-desk1.jf.intel.com ([10.7.198.76]) by orsmga001-auth.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 24 Jul 2019 14:14:43 -0700 Message-ID: Subject: Re: [PATCH v2 QEMU] virtio-balloon: Provide a interface for "bubble hinting" From: Alexander Duyck To: "Michael S. Tsirkin" 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 Date: Wed, 24 Jul 2019 14:14:43 -0700 In-Reply-To: <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> <20190724164433-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.30.5 (3.30.5-1.fc29) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit 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, 2019-07-24 at 16:46 -0400, Michael S. Tsirkin wrote: > 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. I understood that. However it also addresses the shared memory case as well if I recall correctly. Basically any case where us discarding the page could cause issues we should be causing that function to return true.