From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk0-f197.google.com (mail-qk0-f197.google.com [209.85.220.197]) by kanga.kvack.org (Postfix) with ESMTP id 779796B0010 for ; Mon, 23 Jul 2018 10:13:26 -0400 (EDT) Received: by mail-qk0-f197.google.com with SMTP id l11-v6so561819qkk.0 for ; Mon, 23 Jul 2018 07:13:26 -0700 (PDT) Received: from mx1.redhat.com (mx3-rdu2.redhat.com. [66.187.233.73]) by mx.google.com with ESMTPS id b49-v6si2030029qta.299.2018.07.23.07.13.19 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 23 Jul 2018 07:13:19 -0700 (PDT) Date: Mon, 23 Jul 2018 17:13:11 +0300 From: "Michael S. Tsirkin" Subject: Re: [PATCH v36 2/5] virtio_balloon: replace oom notifier with shrinker Message-ID: <20180723170826-mutt-send-email-mst@kernel.org> 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> <5B55AE56.5030404@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5B55AE56.5030404@intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: Wei Wang 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 On Mon, Jul 23, 2018 at 06:30:46PM +0800, Wei Wang wrote: > 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. That's very rare so I won't be too worried. > - 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