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 <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Dave Jiang <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Huang Ying <[email protected]>
Reviewed-by: Jonathan Cameron <[email protected]>
Reviewed-by: David Hildenbrand <[email protected]>
Signed-off-by: Vishal Verma <[email protected]>
---
drivers/dax/bus.c | 40 +++++++++++++++++++++++++++++++++
Documentation/ABI/testing/sysfs-bus-dax | 13 +++++++++++
2 files changed, 53 insertions(+)
diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
index 1ff1ab5fa105..11abb57cc031 100644
--- a/drivers/dax/bus.c
+++ b/drivers/dax/bus.c
@@ -1270,6 +1270,45 @@ 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_region *dax_region = dev_dax->region;
+ ssize_t rc;
+ bool val;
+
+ rc = kstrtobool(buf, &val);
+ if (rc)
+ return rc;
+
+ if (dev_dax->memmap_on_memory == val)
+ return len;
+
+ device_lock(dax_region->dev);
+ if (!dax_region->dev->driver) {
+ device_unlock(dax_region->dev);
+ return -ENXIO;
+ }
+
+ device_lock(dev);
+ dev_dax->memmap_on_memory = val;
+ device_unlock(dev);
+
+ device_unlock(dax_region->dev);
+ return rc == 0 ? len : rc;
+}
+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);
@@ -1296,6 +1335,7 @@ 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 a61a7b186017..bb063a004e41 100644
--- a/Documentation/ABI/testing/sysfs-bus-dax
+++ b/Documentation/ABI/testing/sysfs-bus-dax
@@ -149,3 +149,16 @@ KernelVersion: v5.1
Contact: [email protected]
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: [email protected]
+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).
--
2.41.0
Hi Vishal,
On 07/12/2023 12:36, Vishal Verma wrote:
> +
> +What: /sys/bus/dax/devices/daxX.Y/memmap_on_memory
> +Date: October, 2023
> +KernelVersion: v6.8
> +Contact: [email protected]
> +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
s/memmap_on+memory=1/memmap_on_memory=1
I have a question here
What relationship about memmap_on_memory and 'ndctl-create-namespace -M' option which
specifies where is the vmemmap backed memory.
I'm confused that memmap_on_memory=1 and '-M dev' are the same for nvdimm devdax mode ?
ndctl-create-namespace
...
-M, --map=
A pmem namespace in "fsdax" or "devdax" mode requires allocation of per-page metadata. The allocation
can be drawn from either:
• "mem": typical system memory
• "dev": persistent memory reserved from the namespace :: Given relative capacities of "Persistent
Memory" to "System RAM" the allocation defaults to reserving space out of the namespace directly
("--map=dev"). The overhead is 64-bytes per 4K (16GB per 1TB) on x86.
Thanks
Zhijian
> + placed on regular memory (memmap_on_memory=0). This attribute
> + must be set before the device is handed over to the 'kmem'
On Thu, 2023-12-07 at 08:29 +0000, Zhijian Li (Fujitsu) wrote:
> Hi Vishal,
>
>
> On 07/12/2023 12:36, Vishal Verma wrote:
> > +
> > +What: /sys/bus/dax/devices/daxX.Y/memmap_on_memory
> > +Date: October, 2023
> > +KernelVersion: v6.8
> > +Contact: [email protected]
> > +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
>
> s/memmap_on+memory=1/memmap_on_memory=1
Thanks, will fix.
>
>
> I have a question here
>
> What relationship about memmap_on_memory and 'ndctl-create-namespace
> -M' option which
> specifies where is the vmemmap backed memory.
> I'm confused that memmap_on_memory=1 and '-M dev' are the same for
> nvdimm devdax mode ?
>
The main difference is that memory that comes from non-nvdimm sources,
such as hmem, or cxl, doesn't have a chance to set up the altmaps as
pmem can with '-M dev'. For these, memmap_on_memory does this as part
of the memory hotplug.
Vishal Verma <[email protected]> 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 <[email protected]>
> Cc: Dan Williams <[email protected]>
> Cc: Dave Jiang <[email protected]>
> Cc: Dave Hansen <[email protected]>
> Cc: Huang Ying <[email protected]>
> Reviewed-by: Jonathan Cameron <[email protected]>
> Reviewed-by: David Hildenbrand <[email protected]>
> Signed-off-by: Vishal Verma <[email protected]>
> ---
> drivers/dax/bus.c | 40 +++++++++++++++++++++++++++++++++
> Documentation/ABI/testing/sysfs-bus-dax | 13 +++++++++++
> 2 files changed, 53 insertions(+)
>
> diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> index 1ff1ab5fa105..11abb57cc031 100644
> --- a/drivers/dax/bus.c
> +++ b/drivers/dax/bus.c
> @@ -1270,6 +1270,45 @@ 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_region *dax_region = dev_dax->region;
> + ssize_t rc;
> + bool val;
> +
> + rc = kstrtobool(buf, &val);
> + if (rc)
> + return rc;
> +
> + if (dev_dax->memmap_on_memory == val)
> + return len;
> +
> + device_lock(dax_region->dev);
> + if (!dax_region->dev->driver) {
This still doesn't look right. Can we check whether the current driver
is kmem? And only allow change if it's not kmem?
--
Best Regards,
Huang, Ying
> + device_unlock(dax_region->dev);
> + return -ENXIO;
> + }
> +
> + device_lock(dev);
> + dev_dax->memmap_on_memory = val;
> + device_unlock(dev);
> +
> + device_unlock(dax_region->dev);
> + return rc == 0 ? len : rc;
> +}
> +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);
> @@ -1296,6 +1335,7 @@ 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 a61a7b186017..bb063a004e41 100644
> --- a/Documentation/ABI/testing/sysfs-bus-dax
> +++ b/Documentation/ABI/testing/sysfs-bus-dax
> @@ -149,3 +149,16 @@ KernelVersion: v5.1
> Contact: [email protected]
> 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: [email protected]
> +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).
On 08/12/2023 03:25, Verma, Vishal L wrote:
> On Thu, 2023-12-07 at 08:29 +0000, Zhijian Li (Fujitsu) wrote:
>> Hi Vishal,
>>
>>
>> On 07/12/2023 12:36, Vishal Verma wrote:
>>> +
>>> +What: /sys/bus/dax/devices/daxX.Y/memmap_on_memory
>>> +Date: October, 2023
>>> +KernelVersion: v6.8
>>> +Contact: [email protected]
>>> +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
>>
>> s/memmap_on+memory=1/memmap_on_memory=1
>
> Thanks, will fix.
>>
>>
>> I have a question here
>>
>> What relationship about memmap_on_memory and 'ndctl-create-namespace
>> -M' option which
>> specifies where is the vmemmap backed memory.
>> I'm confused that memmap_on_memory=1 and '-M dev' are the same for
>> nvdimm devdax mode ?
>>
> The main difference is that memory that comes from non-nvdimm sources,
> such as hmem, or cxl, doesn't have a chance to set up the altmaps as
> pmem can with '-M dev'. For these, memmap_on_memory does this as part
> of the memory hotplug.
Thanks for your explanation.
(I wrongly thought nvdimm.kmem was also controlled by '-M dev' before)
feel free add:
Tested-by: Li Zhijian <[email protected]>
On 07.12.23 05:36, Vishal Verma wrote:
> 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 <[email protected]>
> Cc: Dan Williams <[email protected]>
> Cc: Dave Jiang <[email protected]>
> Cc: Dave Hansen <[email protected]>
> Cc: Huang Ying <[email protected]>
> Reviewed-by: Jonathan Cameron <[email protected]>
> Reviewed-by: David Hildenbrand <[email protected]>
> Signed-off-by: Vishal Verma <[email protected]>
> ---
> drivers/dax/bus.c | 40 +++++++++++++++++++++++++++++++++
> Documentation/ABI/testing/sysfs-bus-dax | 13 +++++++++++
> 2 files changed, 53 insertions(+)
>
> diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> index 1ff1ab5fa105..11abb57cc031 100644
> --- a/drivers/dax/bus.c
> +++ b/drivers/dax/bus.c
> @@ -1270,6 +1270,45 @@ 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_region *dax_region = dev_dax->region;
> + ssize_t rc;
> + bool val;
> +
> + rc = kstrtobool(buf, &val);
> + if (rc)
> + return rc;
> +
> + if (dev_dax->memmap_on_memory == val)
> + return len;
> +
> + device_lock(dax_region->dev);
> + if (!dax_region->dev->driver) {
> + device_unlock(dax_region->dev);
> + return -ENXIO;
> + }
> +
> + device_lock(dev);
> + dev_dax->memmap_on_memory = val;
> + device_unlock(dev);
> +
> + device_unlock(dax_region->dev);
> + return rc == 0 ? len : rc;
> +}
> +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);
> @@ -1296,6 +1335,7 @@ 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 a61a7b186017..bb063a004e41 100644
> --- a/Documentation/ABI/testing/sysfs-bus-dax
> +++ b/Documentation/ABI/testing/sysfs-bus-dax
> @@ -149,3 +149,16 @@ KernelVersion: v5.1
> Contact: [email protected]
> 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: [email protected]
> +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).
>
Should we note the dependency on other factors as given in
mhp_supports_memmap_on_memory(), especially, the system-wide setting and
some weird kernel configurations?
--
Cheers,
David / dhildenb
On Fri, 2023-12-08 at 09:20 +0000, Zhijian Li (Fujitsu) wrote:
>
>
> On 08/12/2023 03:25, Verma, Vishal L wrote:
> > On Thu, 2023-12-07 at 08:29 +0000, Zhijian Li (Fujitsu) wrote:
> > > Hi Vishal,
> > >
> > >
> > > On 07/12/2023 12:36, Vishal Verma wrote:
> > > > +
> > > > +What: /sys/bus/dax/devices/daxX.Y/memmap_on_memory
> > > > +Date: October, 2023
> > > > +KernelVersion: v6.8
> > > > +Contact: [email protected]
> > > > +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
> > >
> > > s/memmap_on+memory=1/memmap_on_memory=1
> >
> > Thanks, will fix.
> > >
> > >
> > > I have a question here
> > >
> > > What relationship about memmap_on_memory and 'ndctl-create-namespace
> > > -M' option which
> > > specifies where is the vmemmap backed memory.
> > > I'm confused that memmap_on_memory=1 and '-M dev' are the same for
> > > nvdimm devdax mode ?
> > >
> > The main difference is that memory that comes from non-nvdimm sources,
> > such as hmem, or cxl, doesn't have a chance to set up the altmaps as
> > pmem can with '-M dev'. For these, memmap_on_memory does this as part
> > of the memory hotplug.
>
> Thanks for your explanation.
> (I wrongly thought nvdimm.kmem was also controlled by '-M dev' before)
>
> feel free add:
> Tested-by: Li Zhijian <[email protected]>
Thank you Zhijian!
On Fri, 2023-12-08 at 11:13 +0800, Huang, Ying wrote:
> Vishal Verma <[email protected]> writes:
>
[..]
> >
> > +
> > +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_region *dax_region = dev_dax->region;
> > + ssize_t rc;
> > + bool val;
> > +
> > + rc = kstrtobool(buf, &val);
> > + if (rc)
> > + return rc;
> > +
> > + if (dev_dax->memmap_on_memory == val)
> > + return len;
> > +
> > + device_lock(dax_region->dev);
> > + if (!dax_region->dev->driver) {
>
> This still doesn't look right. Can we check whether the current driver
> is kmem? And only allow change if it's not kmem?
Ah yes I lost track of this todo between revisions when I split this
out. Let me fix that for the next revision.
On Fri, 2023-12-08 at 12:36 +0100, David Hildenbrand wrote:
> On 07.12.23 05:36, Vishal Verma wrote:
[..]
> >
> > +
> > +What: /sys/bus/dax/devices/daxX.Y/memmap_on_memory
> > +Date: October, 2023
> > +KernelVersion: v6.8
> > +Contact: [email protected]
> > +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).
> >
>
> Should we note the dependency on other factors as given in
> mhp_supports_memmap_on_memory(), especially, the system-wide setting and
> some weird kernel configurations?
>
Yep good idea, I'll make a note of those for v3.