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[79.176.41.183]) by smtp.gmail.com with ESMTPSA id 205sm1121279qkd.61.2020.02.06.01.04.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 06 Feb 2020 01:04:25 -0800 (PST) Date: Thu, 6 Feb 2020 04:04:21 -0500 From: "Michael S. Tsirkin" To: Wei Wang Cc: linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, tysand@google.com, david@redhat.com, alexander.h.duyck@linux.intel.com, rientjes@google.com, mhocko@kernel.org, namit@vmware.com, penguin-kernel@i-love.sakura.ne.jp Subject: Re: [PATCH RFC] virtio_balloon: conservative balloon page shrinking Message-ID: <20200206035749-mutt-send-email-mst@kernel.org> References: <1580976107-16013-1-git-send-email-wei.w.wang@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1580976107-16013-1-git-send-email-wei.w.wang@intel.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 06, 2020 at 04:01:47PM +0800, Wei Wang wrote: > There are cases that users want to shrink balloon pages after the > pagecache depleted. The conservative_shrinker lets the shrinker > shrink balloon pages when all the pagecache has been reclaimed. > > Signed-off-by: Wei Wang I'd rather avoid module parameters, but otherwise looks like a reasonable idea. Tyler, what do you think? > --- > drivers/virtio/virtio_balloon.c | 14 +++++++++++++- > 1 file changed, 13 insertions(+), 1 deletion(-) > > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c > index 93f995f6cf36..b4c5bb13a867 100644 > --- a/drivers/virtio/virtio_balloon.c > +++ b/drivers/virtio/virtio_balloon.c > @@ -42,6 +42,10 @@ > static struct vfsmount *balloon_mnt; > #endif > > +static bool conservative_shrinker = true; > +module_param(conservative_shrinker, bool, 0644); > +MODULE_PARM_DESC(conservative_shrinker, "conservatively shrink balloon pages"); > + > enum virtio_balloon_vq { > VIRTIO_BALLOON_VQ_INFLATE, > VIRTIO_BALLOON_VQ_DEFLATE, > @@ -796,6 +800,10 @@ static unsigned long shrink_balloon_pages(struct virtio_balloon *vb, > { > unsigned long pages_freed = 0; > > + /* Balloon pages only gets shrunk when the pagecache depleted */ > + if (conservative_shrinker && global_node_page_state(NR_FILE_PAGES)) > + return 0; > + > /* > * One invocation of leak_balloon can deflate at most > * VIRTIO_BALLOON_ARRAY_PFNS_MAX balloon pages, so we call it > @@ -837,7 +845,11 @@ static unsigned long virtio_balloon_shrinker_count(struct shrinker *shrinker, > struct virtio_balloon, shrinker); > unsigned long count; > > - count = vb->num_pages / VIRTIO_BALLOON_PAGES_PER_PAGE; > + if (conservative_shrinker && global_node_page_state(NR_FILE_PAGES)) I'd rather have an API for that in mm/. In particular, do we want other shrinkers to run, not just pagecache? To pick an example I'm familiar with, kvm mmu cache for nested virt? > + count = 0; > + else > + count = vb->num_pages / VIRTIO_BALLOON_PAGES_PER_PAGE; > + > count += vb->num_free_page_blocks * VIRTIO_BALLOON_HINT_BLOCK_PAGES; > > return count; > -- > 2.17.1