From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wei Wang Subject: Re: [PATCH v36 2/5] virtio_balloon: replace oom notifier with shrinker Date: Mon, 23 Jul 2018 18:30:46 +0800 Message-ID: <5B55AE56.5030404@intel.com> References: <1532075585-39067-1-git-send-email-wei.w.wang@intel.com> <1532075585-39067-3-git-send-email-wei.w.wang@intel.com> <20180722174125-mutt-send-email-mst@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Cc: virtio-dev@lists.oasis-open.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, linux-mm@kvack.org, mhocko@kernel.org, akpm@linux-foundation.org, torvalds@linux-foundation.org, pbonzini@redhat.com, liliang.opensource@gmail.com, yang.zhang.wz@gmail.com, quan.xu0@gmail.com, nilal@redhat.com, riel@redhat.com, peterx@redhat.com To: "Michael S. Tsirkin" Return-path: Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: In-Reply-To: <20180722174125-mutt-send-email-mst@kernel.org> List-Id: kvm.vger.kernel.org On 07/22/2018 10:48 PM, Michael S. Tsirkin wrote: > On Fri, Jul 20, 2018 at 04:33:02PM +0800, Wei Wang wrote: >> >> +static unsigned long virtio_balloon_shrinker_scan(struct shrinker *shrinker, >> + struct shrink_control *sc) >> +{ >> + unsigned long pages_to_free = balloon_pages_to_shrink, >> + pages_freed = 0; >> + struct virtio_balloon *vb = container_of(shrinker, >> + struct virtio_balloon, shrinker); >> + >> + /* >> + * One invocation of leak_balloon can deflate at most >> + * VIRTIO_BALLOON_ARRAY_PFNS_MAX balloon pages, so we call it >> + * multiple times to deflate pages till reaching >> + * balloon_pages_to_shrink pages. >> + */ >> + while (vb->num_pages && pages_to_free) { >> + pages_to_free = balloon_pages_to_shrink - pages_freed; >> + pages_freed += leak_balloon(vb, pages_to_free); >> + } >> + update_balloon_size(vb); > Are you sure that this is never called if count returned 0? Yes. Please see do_shrink_slab, it just returns if count is 0. > >> + >> + return pages_freed / VIRTIO_BALLOON_PAGES_PER_PAGE; >> +} >> + >> +static unsigned long virtio_balloon_shrinker_count(struct shrinker *shrinker, >> + struct shrink_control *sc) >> +{ >> + struct virtio_balloon *vb = container_of(shrinker, >> + struct virtio_balloon, shrinker); >> + >> + /* >> + * We continue to use VIRTIO_BALLOON_F_DEFLATE_ON_OOM to handle the >> + * case when shrinker needs to be invoked to relieve memory pressure. >> + */ >> + if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM)) >> + return 0; > So why not skip notifier registration when deflate on oom > is clear? Sounds good, thanks. > vb->vb_dev_info.inode->i_mapping->a_ops = &balloon_aops; > #endif > + err = virtio_balloon_register_shrinker(vb); > + if (err) > + goto out_del_vqs; > > So we can get scans before device is ready. Leak will fail > then. Why not register later after device is ready? Probably no. - it would be better not to set device ready when register_shrinker failed. - When the device isn't ready, ballooning won't happen, that is, vb->num_pages will be 0, which results in shrinker_count=0 and shrinker_scan won't be called. So I think it would be better to have shrinker registered before device_ready. Best, Wei