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[79.176.6.42]) by smtp.gmail.com with ESMTPSA id u7sm11450091qkm.127.2019.11.19.23.18.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 19 Nov 2019 23:18:32 -0800 (PST) Date: Wed, 20 Nov 2019 02:18:27 -0500 From: "Michael S. Tsirkin" To: linux-kernel@vger.kernel.org Cc: Khazhismel Kumykov , Wei Wang , Jason Wang , virtualization@lists.linux-foundation.org Subject: [PATCH v2] virtio_balloon: fix shrinker scan number of pages Message-ID: <20191120071733.4035-1-mst@redhat.com> MIME-Version: 1.0 X-Mailer: git-send-email 2.22.0.678.g13338e74b8 X-Mutt-Fcc: =sent X-MC-Unique: nDqtpWFnN6yA-8WlhVfjMQ-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org virtio_balloon_shrinker_scan should return number of system pages freed, but because it's calling functions that deal with balloon pages, it gets confused and sometimes returns the number of balloon pages. It does not matter practically as the exact number isn't used, but it seems better to be consistent in case someone starts using this API. Further, if we ever tried to iteratively leak pages as virtio_balloon_shrinker_scan tries to do, we'd run into issues - this is because freed_pages was accumulating total freed pages, but was also subtracted on each iteration from pages_to_free, which can result in either leaking less memory than we were supposed to free, or more if pages_to_free underruns. On a system with 4K pages we are lucky that we are never asked to leak more than 128 pages while we can leak up to 256 at a time, but it looks like a real issue for systems with page size !=3D 4K. Fixes: 71994620bb25 ("virtio_balloon: replace oom notifier with shrinker") Reported-by: Khazhismel Kumykov Reviewed-by: Wei Wang Signed-off-by: Michael S. Tsirkin --- Changes from v1: =09address comment by Khazhismel Kumykov : don't leak more pages than neede= d drivers/virtio/virtio_balloon.c | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-) diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloo= n.c index 226fbb995fb0..51134f9a3ee7 100644 --- a/drivers/virtio/virtio_balloon.c +++ b/drivers/virtio/virtio_balloon.c @@ -772,6 +772,13 @@ static unsigned long shrink_free_pages(struct virtio_b= alloon *vb, =09return blocks_freed << VIRTIO_BALLOON_FREE_PAGE_ORDER; } =20 +static unsigned long leak_balloon_pages(struct virtio_balloon *vb, + unsigned long pages_to_free) +{ +=09return leak_balloon(vb, pages_to_free * VIRTIO_BALLOON_PAGES_PER_PAGE) = / +=09=09VIRTIO_BALLOON_PAGES_PER_PAGE; +} + static unsigned long shrink_balloon_pages(struct virtio_balloon *vb, =09=09=09=09=09 unsigned long pages_to_free) { @@ -782,11 +789,10 @@ static unsigned long shrink_balloon_pages(struct virt= io_balloon *vb, =09 * VIRTIO_BALLOON_ARRAY_PFNS_MAX balloon pages, so we call it =09 * multiple times to deflate pages till reaching pages_to_free. =09 */ -=09while (vb->num_pages && pages_to_free) { -=09=09pages_freed +=3D leak_balloon(vb, pages_to_free) / -=09=09=09=09=09VIRTIO_BALLOON_PAGES_PER_PAGE; -=09=09pages_to_free -=3D pages_freed; -=09} +=09while (vb->num_pages && pages_freed < pages_to_free) +=09=09pages_freed +=3D leak_balloon_pages(vb, +=09=09=09=09=09=09 pages_to_free - pages_freed); + =09update_balloon_size(vb); =20 =09return pages_freed; @@ -799,7 +805,7 @@ static unsigned long virtio_balloon_shrinker_scan(struc= t shrinker *shrinker, =09struct virtio_balloon *vb =3D container_of(shrinker, =09=09=09=09=09struct virtio_balloon, shrinker); =20 -=09pages_to_free =3D sc->nr_to_scan * VIRTIO_BALLOON_PAGES_PER_PAGE; +=09pages_to_free =3D sc->nr_to_scan; =20 =09if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) =09=09pages_freed =3D shrink_free_pages(vb, pages_to_free); --=20 MST