On Tue, Dec 10, 2019 at 08:06:27AM +0000, SeongJae Park wrote:
> Granting pages consumes backend system memory. In systems configured
> with insufficient spare memory for those pages, it can cause a memory
> pressure situation. However, finding the optimal amount of the spare
> memory is challenging for large systems having dynamic resource
> utilization patterns. Also, such a static configuration might lack a
s/lack a/lack/
> flexibility.
>
> To mitigate such problems, this commit adds a memory reclaim callback to
> 'xenbus_driver'. Using this facility, 'xenbus' would be able to monitor
> a memory pressure and request specific devices of specific backend
s/monitor a/monitor/
> drivers which causing the given pressure to voluntarily release its
...which are causing...
> memory.
>
> That said, this commit simply requests every callback registered driver
> to release its memory for every domain, rather than issueing the
s/issueing/issuing/
> requests to the drivers and the domain in charge. Such things will be
I'm afraid I don't understand the "domain in charge" part of this
sentence.
> done in a futur. Also, this commit focuses on memory only. However, it
... done in a future change. Also I think the period after only should
be removed in order to tie both sentences together.
> would be ablt to be extended for general resources.
s/ablt/able/
>
> Signed-off-by: SeongJae Park <sjpark@xxxxxxxxx>
> ---
> drivers/xen/xenbus/xenbus_probe_backend.c | 31 +++++++++++++++++++++++
> include/xen/xenbus.h | 1 +
> 2 files changed, 32 insertions(+)
>
> diff --git a/drivers/xen/xenbus/xenbus_probe_backend.c b/drivers/xen/xenbus/xenbus_probe_backend.c
> index b0bed4faf44c..5a5ba29e39df 100644
> --- a/drivers/xen/xenbus/xenbus_probe_backend.c
> +++ b/drivers/xen/xenbus/xenbus_probe_backend.c
> @@ -248,6 +248,34 @@ static int backend_probe_and_watch(struct notifier_block *notifier,
> return NOTIFY_DONE;
> }
>
> +static int xenbus_backend_reclaim(struct device *dev, void *data)
> +{
> + struct xenbus_driver *drv;
Newline and const.
> + if (!dev->driver)
> + return -ENOENT;
> + drv = to_xenbus_driver(dev->driver);
> + if (drv && drv->reclaim)
> + drv->reclaim(to_xenbus_device(dev));
You seem to completely ignore the return of the reclaim hook...
> + return 0;
> +}
> +
> +/*
> + * Returns 0 always because we are using shrinker to only detect memory
> + * pressure.
> + */
> +static unsigned long xenbus_backend_shrink_count(struct shrinker *shrinker,
> + struct shrink_control *sc)
> +{
> + bus_for_each_dev(&xenbus_backend.bus, NULL, NULL,
> + xenbus_backend_reclaim);
> + return 0;
> +}
> +
> +static struct shrinker xenbus_backend_shrinker = {
> + .count_objects = xenbus_backend_shrink_count,
> + .seeks = DEFAULT_SEEKS,
> +};
> +
> static int __init xenbus_probe_backend_init(void)
> {
> static struct notifier_block xenstore_notifier = {
> @@ -264,6 +292,9 @@ static int __init xenbus_probe_backend_init(void)
>
> register_xenstore_notifier(&xenstore_notifier);
>
> + if (register_shrinker(&xenbus_backend_shrinker))
> + pr_warn("shrinker registration failed\n");
> +
> return 0;
> }
> subsys_initcall(xenbus_probe_backend_init);
> diff --git a/include/xen/xenbus.h b/include/xen/xenbus.h
> index 869c816d5f8c..cdb075e4182f 100644
> --- a/include/xen/xenbus.h
> +++ b/include/xen/xenbus.h
> @@ -104,6 +104,7 @@ struct xenbus_driver {
> struct device_driver driver;
> int (*read_otherend_details)(struct xenbus_device *dev);
> int (*is_ready)(struct xenbus_device *dev);
> + unsigned (*reclaim)(struct xenbus_device *dev);
... hence I wonder why it's returning an unsigned when it's just
ignored.
IMO it should return an int to signal errors, and the return should be
ignored.
Also, I think it would preferable for this function to take an extra
parameter to describe the resource the driver should attempt to free
(ie: memory or interrupts for example). I'm however not able to find
any existing Linux type to describe such resources.
Thanks, Roger.
