Re: [PATCH v3 20/25] dax/bus: Factor out dev dax resize logic

Ira Weiny
2024-08-29T21:38:20Z

Jonathan Cameron wrote:
> On Fri, 16 Aug 2024 09:44:28 -0500
> Ira Weiny <ira.weiny@intel.com> wrote:
>
> > Dynamic Capacity regions must limit dev dax resources to those areas
> > which have extents backing real memory. Such DAX regions are dubbed
> > 'sparse' regions. In order to manage where memory is available four
> > alternatives were considered:
> >
> > 1) Create a single region resource child on region creation which
> > reserves the entire region. Then as extents are added punch holes in
> > this reservation. This requires new resource manipulation to punch
> > the holes and still requires an additional iteration over the extent
> > areas which may already have existing dev dax resources used.
> >
> > 2) Maintain an ordered xarray of extents which can be queried while
> > processing the resize logic. The issue is that existing region->res
> > children may artificially limit the allocation size sent to
> > alloc_dev_dax_range(). IE the resource children can't be directly
> > used in the resize logic to find where space in the region is. This
> > also poses a problem of managing the available size in 2 places.
> >
> > 3) Maintain a separate resource tree with extents. This option is the
> > same as 2) but with the different data structure. Most ideally there
> > should be a unified representation of the resource tree not two places
> > to look for space.
> >
> > 4) Create region resource children for each extent. Manage the dax dev
> > resize logic in the same way as before but use a region child
> > (extent) resource as the parents to find space within each extent.
> >
> > Option 4 can leverage the existing resize algorithm to find space within
> > the extents. It manages the available space in a singular resource tree
> > which is less complicated for finding space.
> >
> > In preparation for this change, factor out the dev_dax_resize logic.
> > For static regions use dax_region->res as the parent to find space for
> > the dax ranges. Future patches will use the same algorithm with
> > individual extent resources as the parent.
> >
> > Signed-off-by: Ira Weiny <ira.weiny@intel.com>
> I'm not 100% confident on this one, so will probably take another look
> before giving a tag.

Thanks.

> One trivial comment below.
>
>
>
> > +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 = dev_dax_size(dev_dax);
> > + struct device *dev = &dev_dax->dev;
> > + resource_size_t alloc = 0;
>
> No path in which this is not set before use.

fixed thanks
Ira

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