[v5,4/4] dax: add a sysfs knob to control memmap_on_memory behavior
Commit Message
Add a sysfs knob for dax devices to control the memmap_on_memory setting
if the dax device were to be hotplugged as system memory.
The default memmap_on_memory setting for dax devices originating via
pmem or hmem is set to 'false' - i.e. no memmap_on_memory semantics, to
preserve legacy behavior. For dax devices via CXL, the default is on.
The sysfs control allows the administrator to override the above
defaults if needed.
Cc: David Hildenbrand <david@redhat.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Huang Ying <ying.huang@intel.com>
Tested-by: Li Zhijian <lizhijian@fujitsu.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
---
drivers/dax/bus.c | 38 +++++++++++++++++++++++++++++++++
Documentation/ABI/testing/sysfs-bus-dax | 17 +++++++++++++++
2 files changed, 55 insertions(+)
Comments
On Thu, Dec 14, 2023 at 12:37:57AM -0700, Vishal Verma wrote:
> +static ssize_t memmap_on_memory_show(struct device *dev,
> + struct device_attribute *attr, char *buf)
> +{
> + struct dev_dax *dev_dax = to_dev_dax(dev);
> +
> + return sprintf(buf, "%d\n", dev_dax->memmap_on_memory);
checkpatch should have noticed that this should be sysfs_emit(), right?
If not, please make the change anyway.
> diff --git a/Documentation/ABI/testing/sysfs-bus-dax b/Documentation/ABI/testing/sysfs-bus-dax
> index 6359f7bc9bf4..40d9965733b2 100644
> --- a/Documentation/ABI/testing/sysfs-bus-dax
> +++ b/Documentation/ABI/testing/sysfs-bus-dax
> @@ -134,3 +134,20 @@ KernelVersion: v5.1
> Contact: nvdimm@lists.linux.dev
> Description:
> (RO) The id attribute indicates the region id of a dax region.
> +
> +What: /sys/bus/dax/devices/daxX.Y/memmap_on_memory
> +Date: October, 2023
It's not October anymore :)
thanks,
greg k-h
Vishal Verma <vishal.l.verma@intel.com> writes:
> Add a sysfs knob for dax devices to control the memmap_on_memory setting
> if the dax device were to be hotplugged as system memory.
>
> The default memmap_on_memory setting for dax devices originating via
> pmem or hmem is set to 'false' - i.e. no memmap_on_memory semantics, to
> preserve legacy behavior. For dax devices via CXL, the default is on.
> The sysfs control allows the administrator to override the above
> defaults if needed.
>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Dave Jiang <dave.jiang@intel.com>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: Huang Ying <ying.huang@intel.com>
> Tested-by: Li Zhijian <lizhijian@fujitsu.com>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Reviewed-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
> ---
> drivers/dax/bus.c | 38 +++++++++++++++++++++++++++++++++
> Documentation/ABI/testing/sysfs-bus-dax | 17 +++++++++++++++
> 2 files changed, 55 insertions(+)
>
> diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> index 6226de131d17..f4d3beec507c 100644
> --- a/drivers/dax/bus.c
> +++ b/drivers/dax/bus.c
> @@ -1245,6 +1245,43 @@ static ssize_t numa_node_show(struct device *dev,
> }
> static DEVICE_ATTR_RO(numa_node);
>
> +static ssize_t memmap_on_memory_show(struct device *dev,
> + struct device_attribute *attr, char *buf)
> +{
> + struct dev_dax *dev_dax = to_dev_dax(dev);
> +
> + return sprintf(buf, "%d\n", dev_dax->memmap_on_memory);
> +}
> +
> +static ssize_t memmap_on_memory_store(struct device *dev,
> + struct device_attribute *attr,
> + const char *buf, size_t len)
> +{
> + struct dev_dax *dev_dax = to_dev_dax(dev);
> + struct dax_device_driver *dax_drv;
> + ssize_t rc;
> + bool val;
> +
> + rc = kstrtobool(buf, &val);
> + if (rc)
> + return rc;
> +
> + if (val == true && !mhp_supports_memmap_on_memory()) {
> + dev_dbg(dev, "memmap_on_memory is not available\n");
> + return -EOPNOTSUPP;
> + }
> +
> + guard(device)(dev);
> + dax_drv = to_dax_drv(dev->driver);
Although "struct driver" is the first member of "struct
dax_device_driver", I feel the code is fragile to depends on that. Can
we check dev->driver directly instead?
--
Best Regards,
Huang, Ying
> + if (dax_drv && dev_dax->memmap_on_memory != val &&
> + dax_drv->type == DAXDRV_KMEM_TYPE)
> + return -EBUSY;
> + dev_dax->memmap_on_memory = val;
> +
> + return len;
> +}
> +static DEVICE_ATTR_RW(memmap_on_memory);
> +
> static umode_t dev_dax_visible(struct kobject *kobj, struct attribute *a, int n)
> {
> struct device *dev = container_of(kobj, struct device, kobj);
> @@ -1271,6 +1308,7 @@ static struct attribute *dev_dax_attributes[] = {
> &dev_attr_align.attr,
> &dev_attr_resource.attr,
> &dev_attr_numa_node.attr,
> + &dev_attr_memmap_on_memory.attr,
> NULL,
> };
>
> diff --git a/Documentation/ABI/testing/sysfs-bus-dax b/Documentation/ABI/testing/sysfs-bus-dax
> index 6359f7bc9bf4..40d9965733b2 100644
> --- a/Documentation/ABI/testing/sysfs-bus-dax
> +++ b/Documentation/ABI/testing/sysfs-bus-dax
> @@ -134,3 +134,20 @@ KernelVersion: v5.1
> Contact: nvdimm@lists.linux.dev
> Description:
> (RO) The id attribute indicates the region id of a dax region.
> +
> +What: /sys/bus/dax/devices/daxX.Y/memmap_on_memory
> +Date: October, 2023
> +KernelVersion: v6.8
> +Contact: nvdimm@lists.linux.dev
> +Description:
> + (RW) Control the memmap_on_memory setting if the dax device
> + were to be hotplugged as system memory. This determines whether
> + the 'altmap' for the hotplugged memory will be placed on the
> + device being hotplugged (memmap_on_memory=1) or if it will be
> + placed on regular memory (memmap_on_memory=0). This attribute
> + must be set before the device is handed over to the 'kmem'
> + driver (i.e. hotplugged into system-ram). Additionally, this
> + depends on CONFIG_MHP_MEMMAP_ON_MEMORY, and a globally enabled
> + memmap_on_memory parameter for memory_hotplug. This is
> + typically set on the kernel command line -
> + memory_hotplug.memmap_on_memory set to 'true' or 'force'."
@@ -1245,6 +1245,43 @@ static ssize_t numa_node_show(struct device *dev,
}
static DEVICE_ATTR_RO(numa_node);
+static ssize_t memmap_on_memory_show(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ struct dev_dax *dev_dax = to_dev_dax(dev);
+
+ return sprintf(buf, "%d\n", dev_dax->memmap_on_memory);
+}
+
+static ssize_t memmap_on_memory_store(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf, size_t len)
+{
+ struct dev_dax *dev_dax = to_dev_dax(dev);
+ struct dax_device_driver *dax_drv;
+ ssize_t rc;
+ bool val;
+
+ rc = kstrtobool(buf, &val);
+ if (rc)
+ return rc;
+
+ if (val == true && !mhp_supports_memmap_on_memory()) {
+ dev_dbg(dev, "memmap_on_memory is not available\n");
+ return -EOPNOTSUPP;
+ }
+
+ guard(device)(dev);
+ dax_drv = to_dax_drv(dev->driver);
+ if (dax_drv && dev_dax->memmap_on_memory != val &&
+ dax_drv->type == DAXDRV_KMEM_TYPE)
+ return -EBUSY;
+ dev_dax->memmap_on_memory = val;
+
+ return len;
+}
+static DEVICE_ATTR_RW(memmap_on_memory);
+
static umode_t dev_dax_visible(struct kobject *kobj, struct attribute *a, int n)
{
struct device *dev = container_of(kobj, struct device, kobj);
@@ -1271,6 +1308,7 @@ static struct attribute *dev_dax_attributes[] = {
&dev_attr_align.attr,
&dev_attr_resource.attr,
&dev_attr_numa_node.attr,
+ &dev_attr_memmap_on_memory.attr,
NULL,
};
@@ -134,3 +134,20 @@ KernelVersion: v5.1
Contact: nvdimm@lists.linux.dev
Description:
(RO) The id attribute indicates the region id of a dax region.
+
+What: /sys/bus/dax/devices/daxX.Y/memmap_on_memory
+Date: October, 2023
+KernelVersion: v6.8
+Contact: nvdimm@lists.linux.dev
+Description:
+ (RW) Control the memmap_on_memory setting if the dax device
+ were to be hotplugged as system memory. This determines whether
+ the 'altmap' for the hotplugged memory will be placed on the
+ device being hotplugged (memmap_on_memory=1) or if it will be
+ placed on regular memory (memmap_on_memory=0). This attribute
+ must be set before the device is handed over to the 'kmem'
+ driver (i.e. hotplugged into system-ram). Additionally, this
+ depends on CONFIG_MHP_MEMMAP_ON_MEMORY, and a globally enabled
+ memmap_on_memory parameter for memory_hotplug. This is
+ typically set on the kernel command line -
+ memory_hotplug.memmap_on_memory set to 'true' or 'force'."