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[79.181.91.42]) by smtp.gmail.com with ESMTPSA id r14sm22913246qke.47.2019.07.24.13.42.32 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Wed, 24 Jul 2019 13:42:36 -0700 (PDT) Date: Wed, 24 Jul 2019 16:42:29 -0400 From: "Michael S. Tsirkin" To: Nitesh Narayan Lal Cc: Alexander Duyck , 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 QEMU] virtio-balloon: Provide a interface for "bubble hinting" Message-ID: <20190724164023-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: 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 04:29:27PM -0400, Nitesh Narayan Lal wrote: > > On 7/24/19 4:18 PM, 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. > I don't think qemu_balloon_is_inhibited() will take care of the page poisoning > situations. > If I am not wrong we may have to look to extend VIRTIO_BALLOON_F_PAGE_POISON > support as per Michael's suggestion. BTW upstream qemu seems to ignore VIRTIO_BALLOON_F_PAGE_POISON ATM. Which is probably a bug. Wei, could you take a look pls? > > > > > -- > Thanks > Nitesh