Re: [PATCH v4 24/28] dax/region: Create resources on sparse DAX regions

Jonathan Cameron
2024-10-10T15:27:49Z

On Mon, 07 Oct 2024 18:16:30 -0500
ira.weiny@intel.com wrote:

> From: Navneet Singh <navneet.singh@intel.com>
>
> DAX regions which map dynamic capacity partitions require that memory be
> allowed to come and go. Recall sparse regions were created for this
> purpose. Now that extents can be realized within DAX regions the DAX
> region driver can start tracking sub-resource information.
>
> The tight relationship between DAX region operations and extent
> operations require memory changes to be controlled synchronously with
> the user of the region. Synchronize through the dax_region_rwsem and by
> having the region driver drive both the region device as well as the
> extent sub-devices.
>
> Recall requests to remove extents can happen at any time and that a host
> is not obligated to release the memory until it is not being used. If
> an extent is not used allow a release response.
>
> The DAX layer has no need for the details of the CXL memory extent
> devices. Expose extents to the DAX layer as device children of the DAX
> region device. A single callback from the driver aids the DAX layer to
> determine if the child device is an extent. The DAX layer also
> registers a devres function to automatically clean up when the device is
> removed from the region.
>
> There is a race between extents being surfaced and the dax_cxl driver
> being loaded. The driver must therefore scan for any existing extents
> while still under the device lock.
>
> Respond to extent notifications. Manage the DAX region resource tree
> based on the extents lifetime. Return the status of remove
> notifications to lower layers such that it can manage the hardware
> appropriately.
>
> Signed-off-by: Navneet Singh <navneet.singh@intel.com>
> Co-developed-by: Ira Weiny <ira.weiny@intel.com>
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
>
More somewhat superficial review from me.
Needs DAX expert reviewers.

Jonathan

> ---
> drivers/cxl/core/extent.c | 74 ++++++++++++--
> drivers/cxl/cxl.h | 6 ++
> drivers/dax/bus.c | 243 +++++++++++++++++++++++++++++++++++++++++-----
> drivers/dax/bus.h | 3 +-
> drivers/dax/cxl.c | 62 +++++++++++-
> drivers/dax/dax-private.h | 42 ++++++++
> drivers/dax/hmem/hmem.c | 2 +-
> drivers/dax/pmem.c | 2 +-
> 8 files changed, 396 insertions(+), 38 deletions(-)
>
> diff --git a/drivers/cxl/core/extent.c b/drivers/cxl/core/extent.c
> index a1eb6e8e4f1a..75fb73ce2185 100644
> --- a/drivers/cxl/core/extent.c
> +++ b/drivers/cxl/core/extent.c
> @@ -270,20 +270,65 @@ static void calc_hpa_range(struct cxl_endpoint_decoder *cxled,
> hpa_range->end = hpa_range->start + range_len(dpa_range) - 1;
> }
>
> +static int cxlr_notify_extent(struct cxl_region *cxlr, enum dc_event event,
> + struct region_extent *region_extent)
> +{
> + struct device *dev = &cxlr->cxlr_dax->dev;
> + struct cxl_notify_data notify_data;
> + struct cxl_driver *driver;
> +
> + dev_dbg(dev, "Trying notify: type %d HPA %pra\n",
> + event, &region_extent->hpa_range);
> +
> + guard(device)(dev);
> +
> + /*
> + * The lack of a driver indicates a notification has failed. No user
> + * space coordiantion was possible.
spell check.
coordination

> + */
> + if (!dev->driver)
> + return 0;
> + driver = to_cxl_drv(dev->driver);
> + if (!driver->notify)
> + return 0;
> +
> + notify_data = (struct cxl_notify_data) {
> + .event = event,
> + .region_extent = region_extent,
> + };
> +
> + dev_dbg(dev, "Notify: type %d HPA %pra\n",
> + event, &region_extent->hpa_range);
> + return driver->notify(dev, &notify_data);
> +}

> diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> index f0e3f8c787df..4e19d18369de 100644
> --- a/drivers/dax/bus.c
> +++ b/drivers/dax/bus.c
> @@ -183,6 +183,86 @@ static bool is_sparse(struct dax_region *dax_region)
> return (dax_region->res.flags & IORESOURCE_DAX_SPARSE_CAP) != 0;
> }

> +
> +int dax_region_add_resource(struct dax_region *dax_region,
> + struct device *device,
> + resource_size_t start, resource_size_t length)
> +{
> + struct resource *new_resource;
> + int rc;
> +
> + struct dax_resource *dax_resource __free(kfree) =
> + kzalloc(sizeof(*dax_resource), GFP_KERNEL);
> + if (!dax_resource)
> + return -ENOMEM;
> +
> + guard(rwsem_write)(&dax_region_rwsem);
> +
> + dev_dbg(dax_region->dev, "DAX region resource %pr\n", &dax_region->res);
> + new_resource = __request_region(&dax_region->res, start, length, "extent", 0);
> + if (!new_resource) {
> + dev_err(dax_region->dev, "Failed to add region s:%pa l:%pa\n",
> + &start, &length);
> + return -ENOSPC;
> + }
> +
> + dev_dbg(dax_region->dev, "add resource %pr\n", new_resource);
> + dax_resource->region = dax_region;
> + dax_resource->res = new_resource;
> + dev_set_drvdata(device, dax_resource);
> + rc = devm_add_action_or_reset(device, dax_release_resource,
> + no_free_ptr(dax_resource));
> + /* On error; ensure driver data is cleared under semaphore */

It's not used in the dax_release_resource callback (that I can
immediately spot) so could you just not set it until after
this has succeeded?

> + if (rc)
> + dev_set_drvdata(device, NULL);
i.e. move
dev_set_drvdata(device, dax_resource);
to here.

> + return rc;
> +}
> +EXPORT_SYMBOL_GPL(dax_region_add_resource);
Adding quite a few exports. Is it time to namespace DAX exports?
Perhaps a follow up series.

> bool static_dev_dax(struct dev_dax *dev_dax)
> {
> return is_static(dev_dax->region);
> @@ -296,19 +376,44 @@ static ssize_t region_align_show(struct device *dev,
> static struct device_attribute dev_attr_region_align =
> __ATTR(align, 0400, region_align_show, NULL);
>
> +#define for_each_child_resource(extent, res) \
> + for (res = (extent)->child; res; res = res->sibling)
> +
Extent naming in here is a little off for a general sounding macro.
Maybe for_each_child_resource(parent, res) or something like that?

Seem generally useful. Maybe move to resource.h?

> @@ -1494,8 +1679,14 @@ 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);
>
> + if (is_sparse(dax_region) && data->size) {
> + dev_err(parent, "Sparse DAX region devices must be created initially with 0 size");
> + rc = -EINVAL;
> + goto err_id;

Right label? This code doesn't have side effects and the next error path is goto err_range
Looks like you fail to reverse the alloc_dev_dax_id() in this error path.

> + }
> +
> rc = alloc_dev_dax_range(&dax_region->res, dev_dax, dax_region->res.start,
> - data->size);
> + data->size, NULL);
> if (rc)
> goto err_range;
>
> diff --git a/drivers/dax/bus.h b/drivers/dax/bus.h
> index 783bfeef42cc..ae5029ea6047 100644
> --- a/drivers/dax/bus.h
> +++ b/drivers/dax/bus.h
> @@ -9,6 +9,7 @@ struct dev_dax;
> struct resource;
> struct dax_device;
> struct dax_region;
> +struct dax_sparse_ops;
>
> /* dax bus specific ioresource flags */
> #define IORESOURCE_DAX_STATIC BIT(0)
> @@ -17,7 +18,7 @@ struct dax_region;
>
> struct dax_region *alloc_dax_region(struct device *parent, int region_id,
> struct range *range, int target_node, unsigned int align,
> - unsigned long flags);
> + unsigned long flags, struct dax_sparse_ops *sparse_ops);
>
> struct dev_dax_data {
> struct dax_region *dax_region;
> diff --git a/drivers/dax/cxl.c b/drivers/dax/cxl.c
> index 367e86b1c22a..df979ea2cb59 100644
> --- a/drivers/dax/cxl.c
> +++ b/drivers/dax/cxl.c
> @@ -5,6 +5,58 @@
>
> #include "../cxl/cxl.h"
> #include "bus.h"
> +#include "dax-private.h"
> +
> +static int __cxl_dax_add_resource(struct dax_region *dax_region,
> + struct region_extent *region_extent)
> +{
> + resource_size_t start, length;
> + struct device *dev;
> +
> + dev = &region_extent->dev;
Might as well do
struct device *dev = &region_extent->dev;

> + start = dax_region->res.start + region_extent->hpa_range.start;
> + length = range_len(&region_extent->hpa_range);
> + return dax_region_add_resource(dax_region, dev, start, length);
> +}

> diff --git a/drivers/dax/dax-private.h b/drivers/dax/dax-private.h
> index ccde98c3d4e2..e3866115243e 100644
> --- a/drivers/dax/dax-private.h
> +++ b/drivers/dax/dax-private.h
...

> +/*
> + * Similar to run_dax() dax_region_{add,rm}_resource() and dax_avail_size() are
> + * exported but are not intended to be generic operations outside the dax
> + * subsystem. They are only generic between the dax layer and the dax drivers.
> + */
> +int dax_region_add_resource(struct dax_region *dax_region, struct device *dev,
> + resource_size_t start, resource_size_t length);
> +int dax_region_rm_resource(struct dax_region *dax_region,
> + struct device *dev);
> +resource_size_t dax_avail_size(struct resource *dax_resource);
> +
> +typedef int (*match_cb)(struct device *dev, resource_size_t *size_avail);
Why is this here?