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

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Date:   Tue, 10 Dec 2019 07:29:52 +0100
From:   SeongJae Park <sj38.park@...il.com>
To:     Jürgen Groß <jgross@...e.com>
Cc:     SeongJae Park <sjpark@...zon.com>, Jens Axboe <axboe@...nel.dk>,
        konrad.wilk@...cle.com, linux-block@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>, pdurrant@...zon.com,
        roger.pau@...rix.com, xen-devel@...ts.xenproject.org,
        SeongJae Park <sjpark@...zon.de>
Subject: Re: [PATCH v4 1/2] xenbus/backend: Add memory pressure handler callback

On Tue, Dec 10, 2019 at 7:23 AM Jürgen Groß <jgross@...e.com> wrote:
>
> On 09.12.19 20:43, SeongJae Park wrote:
> > From: SeongJae Park <sjpark@...zon.de>
> >
> > 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@...zon.de>
> > ---
> >   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?

Oh, I also missed it!  Will do!


Thanks,
SeongJae Park

>
>
> Juergen