On Tue, 22 Sep 2020 09:18:05 +0200 "Jürgen Groß" <jgross@xxxxxxxx> wrote: > On 22.09.20 09:01, SeongJae Park wrote: > > From: SeongJae Park <sjpark@xxxxxxxxx> > > > > Persistent grants feature provides high scalability. On some small > > systems, however, it could incur data copy overhead[1] and thus it is > > required to be disabled. But, there is no option to disable it. For > > the reason, this commit adds a module parameter for disabling of the > > feature. > > > > [1] https://wiki.xen.org/wiki/Xen_4.3_Block_Protocol_Scalability > > > > Signed-off-by: Anthony Liguori <aliguori@xxxxxxxxxx> > > Signed-off-by: SeongJae Park <sjpark@xxxxxxxxx> > > --- > > .../ABI/testing/sysfs-driver-xen-blkback | 8 ++++++++ > > drivers/block/xen-blkback/xenbus.c | 17 ++++++++++++++--- > > 2 files changed, 22 insertions(+), 3 deletions(-) > > > > diff --git a/Documentation/ABI/testing/sysfs-driver-xen-blkback b/Documentation/ABI/testing/sysfs-driver-xen-blkback > > index ecb7942ff146..0c42285c75ee 100644 > > --- a/Documentation/ABI/testing/sysfs-driver-xen-blkback > > +++ b/Documentation/ABI/testing/sysfs-driver-xen-blkback > > @@ -35,3 +35,11 @@ Description: > > controls the duration in milliseconds that blkback will not > > cache any page not backed by a grant mapping. > > The default is 10ms. > > + > > +What: /sys/module/xen_blkback/parameters/feature_persistent > > +Date: September 2020 > > +KernelVersion: 5.10 > > +Contact: SeongJae Park <sjpark@xxxxxxxxx> > > +Description: > > + Whether to enable the persistent grants feature or not. > > + The default is 1 (enable). > > diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c > > index b9aa5d1ac10b..9c03d70469f4 100644 > > --- a/drivers/block/xen-blkback/xenbus.c > > +++ b/drivers/block/xen-blkback/xenbus.c > > @@ -879,6 +879,12 @@ static void reclaim_memory(struct xenbus_device *dev) > > > > /* ** Connection ** */ > > > > +/* Enable the persistent grants feature. */ > > +static unsigned int feature_persistent = 1; > > Use bool, please. Oops, I will. > > > +module_param_named(feature_persistent, feature_persistent, int, 0644); > > module_param() > > > +MODULE_PARM_DESC(feature_persistent, > > + "Enables the persistent grants feature"); > > + > > /* > > * Write the physical details regarding the block device to the store, and > > * switch to Connected state. > > @@ -906,7 +912,8 @@ static void connect(struct backend_info *be) > > > > xen_blkbk_barrier(xbt, be, be->blkif->vbd.flush_support); > > > > - err = xenbus_printf(xbt, dev->nodename, "feature-persistent", "%u", 1); > > + err = xenbus_printf(xbt, dev->nodename, "feature-persistent", "%u", > > + feature_persistent ? 1 : 0); > > Using bool above should allow to just use the value of > feature_persistent here. Indeed. I will fix these as you recommended in the next spin. Thanks, SeongJae Park
