Messages in this thread | | | Date | Sun, 10 May 2015 11:46:19 +0200 | From | Ingo Molnar <> | Subject | Re: "Directly mapped persistent memory page cache" |
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* Dan Williams <dan.j.williams@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
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