Re: [PATCH v4 23/28] dax/bus: Factor out dev dax resize logic

Fan Ni
2024-10-14T16:56:19Z

On Mon, Oct 07, 2024 at 06:16:29PM -0500, Ira Weiny 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>

LGTM based on the code logic, but not familiar with dax resource management.

Fan

> ---
> Changes:
> [Jonathan: Fix handling of alloc]
> ---
> drivers/dax/bus.c | 129 +++++++++++++++++++++++++++++++++---------------------
> 1 file changed, 79 insertions(+), 50 deletions(-)
>
> diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> index d8cb5195a227..f0e3f8c787df 100644
> --- a/drivers/dax/bus.c
> +++ b/drivers/dax/bus.c
> @@ -844,11 +844,9 @@ static int devm_register_dax_mapping(struct dev_dax *dev_dax, int range_id)
> return 0;
> }
>
> -static int alloc_dev_dax_range(struct dev_dax *dev_dax, u64 start,
> - resource_size_t size)
> +static int alloc_dev_dax_range(struct resource *parent, struct dev_dax *dev_dax,
> + u64 start, resource_size_t size)
> {
> - struct dax_region *dax_region = dev_dax->region;
> - struct resource *res = &dax_region->res;
> struct device *dev = &dev_dax->dev;
> struct dev_dax_range *ranges;
> unsigned long pgoff = 0;
> @@ -866,14 +864,14 @@ static int alloc_dev_dax_range(struct dev_dax *dev_dax, u64 start,
> return 0;
> }
>
> - alloc = __request_region(res, start, size, dev_name(dev), 0);
> + alloc = __request_region(parent, start, size, dev_name(dev), 0);
> if (!alloc)
> return -ENOMEM;
>
> ranges = krealloc(dev_dax->ranges, sizeof(*ranges)
> * (dev_dax->nr_range + 1), GFP_KERNEL);
> if (!ranges) {
> - __release_region(res, alloc->start, resource_size(alloc));
> + __release_region(parent, alloc->start, resource_size(alloc));
> return -ENOMEM;
> }
>
> @@ -1026,50 +1024,45 @@ static bool adjust_ok(struct dev_dax *dev_dax, struct resource *res)
> return true;
> }
>
> -static ssize_t dev_dax_resize(struct dax_region *dax_region,
> - struct dev_dax *dev_dax, resource_size_t size)
> +/**
> + * 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.
> + *
> + * @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
> + *
> + * 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)
> {
> - resource_size_t avail = dax_region_avail_size(dax_region), to_alloc;
> - resource_size_t dev_size = dev_dax_size(dev_dax);
> - struct resource *region_res = &dax_region->res;
> - struct device *dev = &dev_dax->dev;
> struct resource *res, *first;
> - resource_size_t alloc = 0;
> int rc;
>
> - if (dev->driver)
> - return -EBUSY;
> - if (size == dev_size)
> - return 0;
> - if (size > dev_size && size - dev_size > avail)
> - return -ENOSPC;
> - if (size < dev_size)
> - return dev_dax_shrink(dev_dax, size);
> -
> - to_alloc = size - dev_size;
> - if (dev_WARN_ONCE(dev, !alloc_is_aligned(dev_dax, to_alloc),
> - "resize of %pa misaligned\n", &to_alloc))
> - return -ENXIO;
> -
> - /*
> - * 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.
> - */
> -retry:
> - first = region_res->child;
> - if (!first)
> - return alloc_dev_dax_range(dev_dax, dax_region->res.start, to_alloc);
> + first = parent->child;
> + if (!first) {
> + rc = alloc_dev_dax_range(parent, dev_dax,
> + parent->start, to_alloc);
> + if (rc)
> + return rc;
> + return to_alloc;
> + }
>
> - rc = -ENOSPC;
> for (res = first; res; res = res->sibling) {
> struct resource *next = res->sibling;
> + resource_size_t alloc;
>
> /* space at the beginning of the region */
> - if (res == first && res->start > dax_region->res.start) {
> - alloc = min(res->start - dax_region->res.start, to_alloc);
> - rc = alloc_dev_dax_range(dev_dax, dax_region->res.start, alloc);
> - break;
> + 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);
> + if (rc)
> + return rc;
> + return alloc;
> }
>
> alloc = 0;
> @@ -1078,21 +1071,55 @@ static ssize_t dev_dax_resize(struct dax_region *dax_region,
> alloc = min(next->start - (res->end + 1), to_alloc);
>
> /* space at the end of the region */
> - if (!alloc && !next && res->end < region_res->end)
> - alloc = min(region_res->end - res->end, to_alloc);
> + if (!alloc && !next && res->end < parent->end)
> + alloc = min(parent->end - res->end, to_alloc);
>
> if (!alloc)
> continue;
>
> if (adjust_ok(dev_dax, res)) {
> rc = adjust_dev_dax_range(dev_dax, res, resource_size(res) + alloc);
> - break;
> + if (rc)
> + return rc;
> + return alloc;
> }
> - rc = alloc_dev_dax_range(dev_dax, res->end + 1, alloc);
> - break;
> + rc = alloc_dev_dax_range(parent, dev_dax, res->end + 1, alloc);
> + if (rc)
> + return rc;
> + return alloc;
> }
> - if (rc)
> - return rc;
> +
> + /* available was already calculated and should never be an issue */
> + dev_WARN_ONCE(&dev_dax->dev, 1, "space not found?");
> + return 0;
> +}
> +
> +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;
> +
> + if (dev->driver)
> + return -EBUSY;
> + if (size == dev_size)
> + return 0;
> + if (size > dev_size && size - dev_size > avail)
> + return -ENOSPC;
> + if (size < dev_size)
> + return dev_dax_shrink(dev_dax, size);
> +
> + to_alloc = size - dev_size;
> + if (dev_WARN_ONCE(dev, !alloc_is_aligned(dev_dax, to_alloc),
> + "resize of %pa misaligned\n", &to_alloc))
> + return -ENXIO;
> +
> +retry:
> + alloc = dev_dax_resize_static(&dax_region->res, dev_dax, to_alloc);
> + if (alloc <= 0)
> + return alloc;
> to_alloc -= alloc;
> if (to_alloc)
> goto retry;
> @@ -1198,7 +1225,8 @@ static ssize_t mapping_store(struct device *dev, struct device_attribute *attr,
>
> to_alloc = range_len(&r);
> if (alloc_is_aligned(dev_dax, to_alloc))
> - rc = alloc_dev_dax_range(dev_dax, r.start, to_alloc);
> + rc = alloc_dev_dax_range(&dax_region->res, dev_dax, r.start,
> + to_alloc);
> up_write(&dax_dev_rwsem);
> up_write(&dax_region_rwsem);
>
> @@ -1466,7 +1494,8 @@ static struct dev_dax *__devm_create_dev_dax(struct dev_dax_data *data)
> device_initialize(dev);
> dev_set_name(dev, "dax%d.%d", dax_region->id, dev_dax->id);
>
> - rc = alloc_dev_dax_range(dev_dax, dax_region->res.start, data->size);
> + rc = alloc_dev_dax_range(&dax_region->res, dev_dax, dax_region->res.start,
> + data->size);
> if (rc)
> goto err_range;
>
>
> --
> 2.46.0
>

--
Fan Ni