On 5/23/26 2:43 AM, Anisa Su wrote:
> A DC dax device's size is determined by the extents that back it, not by
> the user. DCD extents are all-or-nothing, so partial shrink is just as
> illegal as growing. Enforce that on the size and creation paths:
>
> * size_store: any non-zero resize on a DC region returns -EOPNOTSUPP.
> The sole exception is size=0, which daxctl destroy-device writes to
> return every claimed extent to the region's available pool before
> the device's name is written to the region's 'delete' attribute.
> * __devm_create_dev_dax: a DC dax device must be created at size 0.
> Non-zero data->size on a DC region returns -EINVAL with a clear
> message.
>
> The resize machinery (dev_dax_shrink, adjust_ok, dev_dax_resize_static,
> dev_dax_resize) learns to walk the right parent — dax_region->res for
> static regions, the dax_resource->res for DC regions claimed via
> uuid_store — so shrink-to-0 correctly releases each extent's child
> resource rather than the region's.
>
> Based on an original patch by Navneet Singh.
>
> Signed-off-by: Ira Weiny <[email protected]>
> Signed-off-by: Anisa Su <[email protected]>
Reviewed-by: Dave Jiang <[email protected]>
Just a nit below.
>
> ---
> Changes:
> [anisa: split out from the original "Surface dc_extents" commit;
> DC-aware resize policy only.]
> ---
> drivers/dax/bus.c | 46 +++++++++++++++++++++++++++++++++++-----------
> 1 file changed, 35 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> index 1d6f82920be6..c030eb103ad0 100644
> --- a/drivers/dax/bus.c
> +++ b/drivers/dax/bus.c
> @@ -1136,7 +1136,8 @@ static int dev_dax_shrink(struct dev_dax *dev_dax,
> resource_size_t size)
> int i;
>
> for (i = dev_dax->nr_range - 1; i >= 0; i--) {
> - struct range *range = &dev_dax->ranges[i].range;
> + struct dev_dax_range *dev_range = &dev_dax->ranges[i];
> + struct range *range = &dev_range->range;
> struct dax_mapping *mapping = dev_dax->ranges[i].mapping;
> struct resource *adjust = NULL, *res;
> resource_size_t shrink;
> @@ -1152,6 +1153,10 @@ static int dev_dax_shrink(struct dev_dax *dev_dax,
> resource_size_t size)
> continue;
> }
>
> + /*
> + * Partial shrink: forbidden on DC regions, so dev_range
> + * here must belong to a static device.
> + */
> for_each_dax_region_resource(dax_region, res)
> if (strcmp(res->name, dev_name(dev)) == 0
> && res->start == range->start) {
> @@ -1195,19 +1200,21 @@ static bool adjust_ok(struct dev_dax *dev_dax, struct
> resource *res)
> }
>
> /**
> - * dev_dax_resize_static - Expand the device into the unused portion of the
> - * region. This may involve adjusting the end of an existing resource, or
> - * allocating a new resource.
> + * __dev_dax_resize - Expand the device into the unused portion of the
> region.
> + * This may involve adjusting the end of an existing resource, or allocating
> a
> + * new resource.
> *
> * @parent: parent resource to allocate this range in
> * @dev_dax: DAX device to be expanded
> * @to_alloc: amount of space to alloc; must be <= space available in @parent
> + * @dax_resource: if dc; the parent resource
> *
> * Return the amount of space allocated or -ERRNO on failure
> */
> -static ssize_t dev_dax_resize_static(struct resource *parent,
> - struct dev_dax *dev_dax,
> - resource_size_t to_alloc)
> +static ssize_t __dev_dax_resize(struct resource *parent,
> + struct dev_dax *dev_dax,
> + resource_size_t to_alloc,
> + struct dax_resource *dax_resource)
> {
> struct resource *res, *first;
> int rc;
> @@ -1215,7 +1222,8 @@ static ssize_t dev_dax_resize_static(struct resource
> *parent,
> first = parent->child;
> if (!first) {
> rc = alloc_dev_dax_range(parent, dev_dax,
> - parent->start, to_alloc, NULL);
> + parent->start, to_alloc,
> + dax_resource);
> if (rc)
> return rc;
> return to_alloc;
> @@ -1229,7 +1237,8 @@ static ssize_t dev_dax_resize_static(struct resource
> *parent,
> if (res == first && res->start > parent->start) {
> alloc = min(res->start - parent->start, to_alloc);
> rc = alloc_dev_dax_range(parent, dev_dax,
> - parent->start, alloc, NULL);
> + parent->start, alloc,
> + dax_resource);
> if (rc)
> return rc;
> return alloc;
> @@ -1253,7 +1262,8 @@ static ssize_t dev_dax_resize_static(struct resource
> *parent,
> return rc;
> return alloc;
> }
> - rc = alloc_dev_dax_range(parent, dev_dax, res->end + 1, alloc,
> NULL);
> + rc = alloc_dev_dax_range(parent, dev_dax, res->end + 1, alloc,
> + dax_resource);
> if (rc)
> return rc;
> return alloc;
> @@ -1264,6 +1274,13 @@ static ssize_t dev_dax_resize_static(struct resource
> *parent,
> return 0;
> }
>
> +static ssize_t dev_dax_resize_static(struct dax_region *dax_region,
> + struct dev_dax *dev_dax,
> + resource_size_t to_alloc)
> +{
> + return __dev_dax_resize(&dax_region->res, dev_dax, to_alloc, NULL);
> +}
> +
> static ssize_t dev_dax_resize(struct dax_region *dax_region,
> struct dev_dax *dev_dax, resource_size_t size)
> {
> @@ -1277,6 +1294,8 @@ static ssize_t dev_dax_resize(struct dax_region
> *dax_region,
> return -EBUSY;
> if (size == dev_size)
> return 0;
> + if (size != 0 && is_dynamic(dax_region))
> + return -EOPNOTSUPP;
> if (size > dev_size && size - dev_size > avail)
> return -ENOSPC;
> if (size < dev_size)
> @@ -1288,7 +1307,7 @@ static ssize_t dev_dax_resize(struct dax_region
> *dax_region,
> return -ENXIO;
>
> retry:
> - alloc = dev_dax_resize_static(&dax_region->res, dev_dax, to_alloc);
> + alloc = dev_dax_resize_static(dax_region, dev_dax, to_alloc);
> if (alloc <= 0)
> return alloc;
> to_alloc -= alloc;
> @@ -1674,6 +1693,11 @@ static struct dev_dax *__devm_create_dev_dax(struct
> dev_dax_data *data)
> struct device *dev;
> int rc;
>
> + if (is_dynamic(dax_region) && data->size) {
> + dev_err(parent, "DC DAX region devices must be created
> initially with 0 size");
Needs \n
> + return ERR_PTR(-EINVAL);
> + }
> +
> dev_dax = kzalloc_obj(*dev_dax);
> if (!dev_dax)
> return ERR_PTR(-ENOMEM);
