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dax: add a sysfs knob to control memmap_on_memory behavior

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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.

Link: https://lkml.kernel.org/r/20240124-vv-dax_abi-v7-5-20d16cb8d23d@intel.com
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
Tested-by: Li Zhijian <lizhijian@fujitsu.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Huang, Ying <ying.huang@intel.com>
Reviewed-by: Alison Schofield <alison.schofield@intel.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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Oscar Salvador <osalvador@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Vishal Verma 2024-01-24 12:03:50 -08:00 committed by Andrew Morton
parent 42d9358252
commit 73954d379e
2 changed files with 60 additions and 0 deletions
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17
Documentation/ABI/testing/sysfs-bus-dax
View File

@ -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: January, 2024
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'."

43
drivers/dax/bus.c
View File

@ -1349,6 +1349,48 @@ 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 sysfs_emit(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);
bool val;
int rc;
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;
}
rc = down_write_killable(&dax_dev_rwsem);
if (rc)
return rc;
if (dev_dax->memmap_on_memory != val && dev->driver &&
to_dax_drv(dev->driver)->type == DAXDRV_KMEM_TYPE) {
up_write(&dax_dev_rwsem);
return -EBUSY;
}
dev_dax->memmap_on_memory = val;
up_write(&dax_dev_rwsem);
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);
@ -1375,6 +1417,7 @@ 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,
};