Dan Williams <dan.j.willi...@intel.com> writes: > On Wed, Oct 30, 2019 at 10:35 PM Aneesh Kumar K.V > <aneesh.ku...@linux.ibm.com> wrote: > [..] >> > True, for the pfn device and the device-dax mapping size, but I'm >> > suggesting adding another instance of alignment control at the raw >> > namespace level. That would need to be disconnected from the >> > device-dax page mapping granularity. >> > >> >> Can you explain what you mean by raw namespace level ? We don't have >> multiple values against which we need to check the alignment of >> namespace start and namespace size. >> >> If you can outline how and where you would like to enforce that check I >> can start working on it. >> > > What I mean is that the process of setting up a pfn namespace goes > something like this in shell script form: > > 1/ echo $size > /sys/bus/nd/devices/$namespace/size > 2/ echo $namespace > /sys/bus/nd/devices/$pfn/namespace > 3/ echo $pfn_align > /sys/bus/nd/devices/$pfn/align > > What I'm suggesting is add an optional 0th step that does: > > echo $raw_align > /sys/bus/nd/devices/$namespace/align > > Where the raw align needs to be needs to be max($pfn_align, > arch_mapping_granulariy).
I started looking at this and was wondering about userspace being aware of the direct-map mapping size. We can figure that out by parsing kernel log [ 0.000000] Page orders: linear mapping = 24, virtual = 16, io = 16, vmemmap = 24 But I am not sure we want to do that. There is not set of raw_align value to select. What we need to make sure is the below. 1) While creating a namespace we need to make sure that namespace size is multiple of direct-map mapping size. If we ensure that size is aligned, we should also get the namespace start to be aligned? 2) While initialzing a namespace by scanning label area, we need to make sure every namespace in the region satisfy the above requirement. If not we should mark the region disabled. > > So on powerpc where PAGE_SIZE < arch_mapping_granulariy, the following: > > cat /sys/bus/nd/devices/$namespace/supported_aligns > > ...would show the same output as: > > cat /sys/bus/nd/devices/$pfn/align > > ...but with any alignment choice less than arch_mapping_granulariy removed. > I am not sure why we need to do that. For example: even if we have direct-map mapping size as PAGE_SIZE (64K), we still should allow an user mapping with hugepage size (16M)? -aneesh
