On Thu, Apr 27, 2017 at 8:59 AM, Dan Williams <[email protected]> wrote:
> On Thu, Apr 27, 2017 at 2:15 AM, Oliver O'Halloran <[email protected]> wrote:
>> Adds two new sysfs attributes for pfn (and dax) devices:
>> supported_alignements and default_alignment. These advertise to
>> userspace what alignments this kernel supports, and provides a nominal
>> default alignment to use.
>>
>> Signed-off-by: Oliver O'Halloran <[email protected]>
>> ---
>> I'm not sure it makes sense to provide these for pfn devices. In the dax
>> case we have hard restrictions because of how fault handling works, but
>> I'm not convinced this makes sense for the pfn case since it's going to
>> be used with fs-dax.
>
> We still want this for fs-dax so we can make sure that the namespace
> is aligned to allow for opportunistic large mappings. We have pmd
> support for fs-dax currently shipping, and looking to expand that to
> pud support.
>
>> ---
>> drivers/nvdimm/pfn_devs.c | 26 ++++++++++++++++++++++++++
>> 1 file changed, 26 insertions(+)
>>
>> diff --git a/drivers/nvdimm/pfn_devs.c b/drivers/nvdimm/pfn_devs.c
>> index 6c033c9a2f06..5157e7d89f0b 100644
>> --- a/drivers/nvdimm/pfn_devs.c
>> +++ b/drivers/nvdimm/pfn_devs.c
>> @@ -260,6 +260,30 @@ static ssize_t size_show(struct device *dev,
>> }
>> static DEVICE_ATTR_RO(size);
>>
>> +static ssize_t supported_alignments_show(struct device *dev,
>> + struct device_attribute *attr, char *buf)
>> +{
>> + /* Fun fact: These aren't always constants! */
>> + unsigned long supported_alignments[] = {
>> + PAGE_SIZE,
>> + HPAGE_PMD_SIZE,
>> +#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
>> + HPAGE_PUD_SIZE,
>> +#endif
>> + 0,
>> + };
>> +
>> + return nd_sector_size_show(0, supported_alignments, buf);
>> +}
>> +DEVICE_ATTR_RO(supported_alignments);
>> +
>> +static ssize_t default_alignment_show(struct device *dev,
>> + struct device_attribute *attr, char *buf)
>> +{
>> + return sprintf(buf, "%ld\n", HPAGE_PMD_SIZE);
>> +}
>> +DEVICE_ATTR_RO(default_alignment);
>> +
>> static struct attribute *nd_pfn_attributes[] = {
>> &dev_attr_mode.attr,
>> &dev_attr_namespace.attr,
>> @@ -267,6 +291,8 @@ static struct attribute *nd_pfn_attributes[] = {
>> &dev_attr_align.attr,
>> &dev_attr_resource.attr,
>> &dev_attr_size.attr,
>> + &dev_attr_supported_alignments.attr,
>> + &dev_attr_default_alignment.attr,
>> NULL,
>
> So, we don't need DEVICE_ATTR_RO(default_alignment), that can be
> reflected by setting nd_pfn->align to HPAGE_PMD_SIZE by default and
> passing nd_pfn->align to nd_sector_size_show(). Should probably rename
> nd_sector_size_show() to nd_size_select_show().
>
> The other concern is that the current DEVICE_ATTR_RW(align) can be
> made redundant by this new interface if you make it writable. I wonder
> if we can avoid breaking old ndctl versions by making the current
> align setting the first one in the output? Worse comes to worse we can
> live with two attributes 'align' and 'aligns', but I'd like to see if
> can add this to the existing attribute.
Ok, so we can make this backward compatible, all that is needed is to
list the current setting as the first entry in the list and make it
un-decorated. For example a size list like this with 528 selected:
"512 520 [528] 4096 4104 4160 4224"
...would become this:
"528 512 520 [528] 4096 4104 4160 4224"
...slightly messy, but it allows us to avoid growing redundant attributes.
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