On 6/30/26 2:18 PM, Gregory Price wrote:
> Refactor kmem _probe() _remove() by extracting init, cleanup, hotplug,
> and hot-remove logic into separate helper functions:
>
> - dax_kmem_init_resources: inits IO_RESOURCE w/ request_mem_region
> - dax_kmem_cleanup_resources: cleans up initialized IO_RESOURCE
> - dax_kmem_do_hotplug: handles memory region reservation and adding
> - dax_kmem_do_hotremove: handles memory removal and resource cleanup
>
> This is a pure refactoring with no functional change. The helpers will
> enable future extensions to support more granular control over memory
> hotplug operations.
>
> We need to split hotplug/hotunplug and init/cleanup in order to have the
> resources available for hot-add. Otherwise, when probe occurs, the dax
> devices are never added to sysfs because the resources are never
> registered.
>
> Detatching hotunplug/cleanup allows us to re-use the hotunplug code
> without destroying the underlying resources.
>
> Signed-off-by: Gregory Price <[email protected]>
Minor comment below
Reviewed-by: Dave Jiang <[email protected]>
> ---
> drivers/dax/kmem.c | 327 +++++++++++++++++++++++++++++++--------------
> 1 file changed, 225 insertions(+), 102 deletions(-)
>
> diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
> index 0a184c0878dd..72dcccee41e1 100644
> --- a/drivers/dax/kmem.c
> +++ b/drivers/dax/kmem.c
> @@ -63,14 +63,206 @@ static void kmem_put_memory_types(void)
> mt_put_memory_types(&kmem_memory_types);
> }
>
> +/**
> + * dax_kmem_do_hotplug - hotplug memory for dax kmem device
> + * @dev_dax: the dev_dax instance
> + * @data: the dax_kmem_data structure with resource tracking
> + *
> + * Hotplugs all ranges in the dev_dax region as system memory.
> + *
> + * Returns the number of successfully mapped ranges, or negative error.
> + */
> +static int dax_kmem_do_hotplug(struct dev_dax *dev_dax,
> + struct dax_kmem_data *data,
> + int online_type)
> +{
> + struct device *dev = &dev_dax->dev;
> + int i, rc, onlined = 0;
> + mhp_t mhp_flags;
> +
> + for (i = 0; i < dev_dax->nr_range; i++) {
> + struct range range;
> +
> + rc = dax_kmem_range(dev_dax, i, &range);
> + if (rc)
> + continue;
> +
> + /*
> + * init_resources() is best-effort: if a reservation conflict
> + * occurs it keeps the range but leaves res[i]=NULL. For hotplug
> + * on probe systems, this means kmem will partially online.
> + *
> + * We have to keep this behavior not to break those systems.
> + * For those systems - atomicity only applies to valid ranges.
> + */
> + if (!data->res[i])
> + continue;
> +
> + mhp_flags = MHP_NID_IS_MGID;
> + if (dev_dax->memmap_on_memory)
> + mhp_flags |= MHP_MEMMAP_ON_MEMORY;
> +
> + /*
> + * Ensure that future kexec'd kernels will not treat
> + * this as RAM automatically.
> + */
> + rc = __add_memory_driver_managed(data->mgid, range.start,
> + range_len(&range), kmem_name, mhp_flags,
> + online_type);
> +
> + if (rc) {
> + dev_warn(dev, "mapping%d: %#llx-%#llx memory add
> failed\n",
> + i, range.start, range.end);
> + /*
> + * Release the reservation for the range that failed to
> + * add so a later hotremove does not try to remove
> memory
> + * that was never added.
> + */
> + if (data->res[i]) {
> + remove_resource(data->res[i]);
> + kfree(data->res[i]);
> + data->res[i] = NULL;
> + }
> + if (onlined)
> + continue;
> + return rc;
> + }
> + onlined++;
> + }
> +
> + return onlined;
> +}
> +
> +/**
> + * dax_kmem_init_resources - create memory regions for dax kmem
> + * @dev_dax: the dev_dax instance
> + * @data: the dax_kmem_data structure with resource tracking
> + *
> + * Initializes all the resources for the DAX
> + *
> + * Returns the number of successfully mapped ranges, or negative error.
> + */
> +static int dax_kmem_init_resources(struct dev_dax *dev_dax,
> + struct dax_kmem_data *data)
> +{
> + struct device *dev = &dev_dax->dev;
> + int i, rc, mapped = 0;
> +
> + for (i = 0; i < dev_dax->nr_range; i++) {
> + struct resource *res;
> + struct range range;
> +
> + rc = dax_kmem_range(dev_dax, i, &range);
> + if (rc)
> + continue;
> +
> + /* Skip ranges already added */
> + if (data->res[i])
> + continue;
> +
> + /* Region is permanently reserved if hotremove fails. */
> + res = request_mem_region(range.start, range_len(&range),
> + data->res_name);
> + if (!res) {
> + dev_warn(dev, "mapping%d: %#llx-%#llx could not reserve
> region\n",
> + i, range.start, range.end);
> + /*
> + * Once some memory has been onlined we can't
> + * assume that it can be un-onlined safely.
> + */
> + if (mapped)
> + continue;
> + return -EBUSY;
> + }
> + data->res[i] = res;
> + /*
> + * Set flags appropriate for System RAM. Leave ..._BUSY clear
> + * so that add_memory() can add a child resource. Do not
> + * inherit flags from the parent since it may set new flags
> + * unknown to us that will break add_memory() below.
'later' instead of 'below'? Comment reflects previous function flow that is no
longer the case.
DJ
> + */
> + res->flags = IORESOURCE_SYSTEM_RAM;
> + mapped++;
> + }
> + return mapped;
> +}
> +
> +#ifdef CONFIG_MEMORY_HOTREMOVE
> +/**
> + * dax_kmem_do_hotremove - hot-remove memory for dax kmem device
> + * @dev_dax: the dev_dax instance
> + * @data: the dax_kmem_data structure with resource tracking
> + *
> + * Removes all ranges in the dev_dax region.
> + *
> + * Returns the number of successfully removed ranges.
> + */
> +static int dax_kmem_do_hotremove(struct dev_dax *dev_dax,
> + struct dax_kmem_data *data)
> +{
> + struct device *dev = &dev_dax->dev;
> + int i, success = 0;
> +
> + for (i = 0; i < dev_dax->nr_range; i++) {
> + struct range range;
> + int rc;
> +
> + rc = dax_kmem_range(dev_dax, i, &range);
> + if (rc)
> + continue;
> +
> + /* range was never added during probe, count as removed */
> + if (!data->res[i]) {
> + success++;
> + continue;
> + }
> +
> + rc = remove_memory(range.start, range_len(&range));
> + if (rc == 0) {
> + /* Release the resource for the successfully removed
> range */
> + remove_resource(data->res[i]);
> + kfree(data->res[i]);
> + data->res[i] = NULL;
> + success++;
> + continue;
> + }
> + any_hotremove_failed = true;
> + dev_err(dev, "mapping%d: %#llx-%#llx hotremove failed\n",
> + i, range.start, range.end);
> + }
> +
> + return success;
> +}
> +#endif /* CONFIG_MEMORY_HOTREMOVE */
> +
> +/**
> + * dax_kmem_cleanup_resources - remove the dax memory resources
> + * @dev_dax: the dev_dax instance
> + * @data: the dax_kmem_data structure with resource tracking
> + *
> + * Removes all resources in the dev_dax region.
> + */
> +static void dax_kmem_cleanup_resources(struct dev_dax *dev_dax,
> + struct dax_kmem_data *data)
> +{
> + int i;
> +
> + for (i = 0; i < dev_dax->nr_range; i++) {
> + if (!data->res[i])
> + continue;
> + remove_resource(data->res[i]);
> + kfree(data->res[i]);
> + data->res[i] = NULL;
> + }
> +}
> +
> static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
> {
> struct device *dev = &dev_dax->dev;
> unsigned long total_len = 0, orig_len = 0;
> struct dax_kmem_data *data;
> struct memory_dev_type *mtype;
> - int i, rc, mapped = 0;
> - mhp_t mhp_flags;
> + int i, rc;
> int numa_node;
> int online_type;
> int adist = MEMTIER_DEFAULT_DAX_ADISTANCE;
> @@ -133,73 +325,27 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
> goto err_reg_mgid;
> data->mgid = rc;
>
> + dev_set_drvdata(dev, data);
> +
> + rc = dax_kmem_init_resources(dev_dax, data);
> + if (rc < 0)
> + goto err_resources;
> +
> /* Resolve system default at bind time in case it changed */
> online_type = dev_dax->online_type;
> if (online_type == DAX_ONLINE_DEFAULT)
> online_type = mhp_get_default_online_type();
>
> - for (i = 0; i < dev_dax->nr_range; i++) {
> - struct resource *res;
> - struct range range;
> -
> - rc = dax_kmem_range(dev_dax, i, &range);
> - if (rc)
> - continue;
> -
> - /* Region is permanently reserved if hotremove fails. */
> - res = request_mem_region(range.start, range_len(&range),
> data->res_name);
> - if (!res) {
> - dev_warn(dev, "mapping%d: %#llx-%#llx could not reserve
> region\n",
> - i, range.start, range.end);
> - /*
> - * Once some memory has been onlined we can't
> - * assume that it can be un-onlined safely.
> - */
> - if (mapped)
> - continue;
> - rc = -EBUSY;
> - goto err_request_mem;
> - }
> - data->res[i] = res;
> -
> - /*
> - * Set flags appropriate for System RAM. Leave ..._BUSY clear
> - * so that add_memory() can add a child resource. Do not
> - * inherit flags from the parent since it may set new flags
> - * unknown to us that will break add_memory() below.
> - */
> - res->flags = IORESOURCE_SYSTEM_RAM;
> -
> - mhp_flags = MHP_NID_IS_MGID;
> - if (dev_dax->memmap_on_memory)
> - mhp_flags |= MHP_MEMMAP_ON_MEMORY;
> -
> - /*
> - * Ensure that future kexec'd kernels will not treat
> - * this as RAM automatically.
> - */
> - rc = __add_memory_driver_managed(data->mgid, range.start,
> - range_len(&range), kmem_name, mhp_flags,
> - online_type);
> -
> - if (rc) {
> - dev_warn(dev, "mapping%d: %#llx-%#llx memory add
> failed\n",
> - i, range.start, range.end);
> - remove_resource(res);
> - kfree(res);
> - data->res[i] = NULL;
> - if (mapped)
> - continue;
> - goto err_request_mem;
> - }
> - mapped++;
> - }
> -
> - dev_set_drvdata(dev, data);
> + rc = dax_kmem_do_hotplug(dev_dax, data, online_type);
> + if (rc < 0)
> + goto err_hotplug;
>
> return 0;
>
> -err_request_mem:
> +err_hotplug:
> + dax_kmem_cleanup_resources(dev_dax, data);
> +err_resources:
> + dev_set_drvdata(dev, NULL);
> memory_group_unregister(data->mgid);
> err_reg_mgid:
> kfree(data->res_name);
> @@ -213,7 +359,7 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
> #ifdef CONFIG_MEMORY_HOTREMOVE
> static void dev_dax_kmem_remove(struct dev_dax *dev_dax)
> {
> - int i, success = 0;
> + int success;
> int node = dev_dax->target_node;
> struct device *dev = &dev_dax->dev;
> struct dax_kmem_data *data = dev_get_drvdata(dev);
> @@ -224,48 +370,25 @@ static void dev_dax_kmem_remove(struct dev_dax *dev_dax)
> * there is no way to hotremove this memory until reboot because device
> * unbind will succeed even if we return failure.
> */
> - for (i = 0; i < dev_dax->nr_range; i++) {
> - struct range range;
> - int rc;
> -
> - rc = dax_kmem_range(dev_dax, i, &range);
> - if (rc)
> - continue;
> -
> - /* range was never added during probe */
> - if (!data->res[i]) {
> - success++;
> - continue;
> - }
> -
> - rc = remove_memory(range.start, range_len(&range));
> - if (rc == 0) {
> - remove_resource(data->res[i]);
> - kfree(data->res[i]);
> - data->res[i] = NULL;
> - success++;
> - continue;
> - }
> - any_hotremove_failed = true;
> - dev_err(dev,
> - "mapping%d: %#llx-%#llx cannot be hotremoved until the
> next reboot\n",
> - i, range.start, range.end);
> + success = dax_kmem_do_hotremove(dev_dax, data);
> + if (success < dev_dax->nr_range) {
> + dev_err(dev, "Hotplug regions stuck online until reboot\n");
> + return;
> }
>
> - if (success >= dev_dax->nr_range) {
> - memory_group_unregister(data->mgid);
> - kfree(data->res_name);
> - kfree(data);
> - dev_set_drvdata(dev, NULL);
> - /*
> - * Clear the memtype association on successful unplug.
> - * If not, we have memory blocks left which can be
> - * offlined/onlined later. We need to keep memory_dev_type
> - * for that. This implies this reference will be around
> - * till next reboot.
> - */
> - clear_node_memory_type(node, NULL);
> - }
> + dax_kmem_cleanup_resources(dev_dax, data);
> + memory_group_unregister(data->mgid);
> + kfree(data->res_name);
> + kfree(data);
> + dev_set_drvdata(dev, NULL);
> + /*
> + * Clear the memtype association on successful unplug.
> + * If not, we have memory blocks left which can be
> + * offlined/onlined later. We need to keep memory_dev_type
> + * for that. This implies this reference will be around
> + * till next reboot.
> + */
> + clear_node_memory_type(node, NULL);
> }
> #else
> static void dev_dax_kmem_remove(struct dev_dax *dev_dax)
