linux-kernel - Re: [PATCH 11/12] device-dax: Add dis-contiguous resource support

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Message-ID: <CAPcyv4gBQOh9sba+Zbpo6yw3sh9JCKC7Cd10qdNc7d1TvTFfYQ@mail.gmail.com>
Date:   Wed, 25 Mar 2020 10:48:58 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Joao Martins <joao.m.martins@...cle.com>
Cc:     Linux MM <linux-mm@...ck.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Christoph Hellwig <hch@....de>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 11/12] device-dax: Add dis-contiguous resource support

On Wed, Mar 25, 2020 at 3:35 AM Joao Martins <joao.m.martins@...cle.com> wrote:
>
> On 3/24/20 4:12 PM, Joao Martins wrote:
> > On 3/23/20 11:55 PM, Dan Williams wrote:
> >>  static ssize_t dev_dax_resize(struct dax_region *dax_region,
> >>              struct dev_dax *dev_dax, resource_size_t size)
> >>  {
> >>      resource_size_t avail = dax_region_avail_size(dax_region), to_alloc;
> >> -    resource_size_t dev_size = range_len(&dev_dax->range);
> >> +    resource_size_t dev_size = dev_dax_size(dev_dax);
> >>      struct resource *region_res = &dax_region->res;
> >>      struct device *dev = &dev_dax->dev;
> >> -    const char *name = dev_name(dev);
> >>      struct resource *res, *first;
> >> +    resource_size_t alloc = 0;
> >> +    int rc;
> >>
> >>      if (dev->driver)
> >>              return -EBUSY;
> >> @@ -684,38 +766,47 @@ static ssize_t dev_dax_resize(struct dax_region *dax_region,
> >>       * allocating a new resource.
> >>       */
> >>      first = region_res->child;
> >> -    if (!first)
> >> -            return __alloc_dev_dax_range(dev_dax, dax_region->res.start,
> >> -                            to_alloc);
> >
> > You probably want to retain the condition above?
> >
> > Otherwise it removes the ability to create new devices or resizing it , once we
> > have zero-ed the last one.
> >
>
> A quick unit test that I had stashed here to help explain what I mean:
>
>         cd /sys/bus/dax/devices
>         # dax0.0 is the only dax device in the corresponding dax_region
>         echo dax0.0 > dax0.0/driver/unbind
>         echo 0 > dax0.0/size
>         # Shouldn't fail but returns -ENOSPC despite having
>         # the full region available
>         cat $(readlink -f dax0.0/../dax_region/available_size) > dax0.0/size

Thanks! Will incorporate that test before resending the series.