Re: [Xen-devel] [PATCH v4 1/2] xenbus/backend: Add memory pressure handler callback

[Jürgen Groß <jgross@xxxxxxxx>]

On 09.12.19 20:43, SeongJae Park wrote:
> From: SeongJae Park <sjpark@xxxxxxxxx>
>
> 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 lacks a
> 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 domains of specific backend
> drivers which causing the given pressure to voluntarily release its
> memory.
>
> That said, this commit simply requests every callback registered driver
> to release its memory for every domain, rather than issueing the
> requests to the drivers and domain in charge.  Such things would be a
> future work.  Also, this commit focuses on memory only.  However, it
> would be ablt to be extended for general resources.
>
> 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..cd5fd1cd8de3 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;
> +       if (!dev->driver)
> +               return -ENOENT;
> +       drv = to_xenbus_driver(dev->driver);
> +       if (drv && drv->reclaim)
> +               drv->reclaim(to_xenbus_device(dev), DOMID_INVALID);
Oh, sorry for first requesting you to add the domid as a parameter,
but now I realize this could be handled in the xenbus driver, as
struct xenbus_device already contains the otherend_id.

Would you mind dropping the parameter again, please?


Juergen

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