9:46 a.m.
* Dan Williams <dan.j.williams(a)intel.com> wrote:
> "Directly mapped pmem integrated into the page
cache":
> ------------------------------------------------------
Nice, I think it makes sense as an area that gets reserved at file
system creation time. You are not proposing that this gets
automatically reserved at the device level, right? [...]
Well, it's most practical if the device does it automatically (the
layout is determined prior filesystem creation), and the filesystem
does not necessarily have to be aware of it - but obviously as a user
opt-in.
[...] For the use cases of persistent memory in the absence of a
file system (in-kernel managed hierarchical storage driver, or
mmap() the pmem block device directly) there's still a need for
pfn-based DAX. [...]
Yes, but knowing that there's a sane model we can take a hard stance
against pfn proliferation and say: 'we let pfns this far and no
farther'.
[...] In other words, simple usages skip the overhead. They assume
pfns only, discover those pmem pfns via ->direct_access(), and
arrange for exclusive block device ownership. Everything else that
requires struct page in turn requires a file system to have opt-ed
into this reservation and provide pmem-struct-page infrastructure,
pmem-aware-DIO etc.
Yes.
Thanks,
Ingo