Re: DAX mapping detection (was: Re: [PATCH] Fix region lost in /proc/self/smaps)

From	Xiao Guangrong <guangrong.xiao@linux.intel.com>
Newsgroups	linux.kernel
Subject	Re: DAX mapping detection (was: Re: [PATCH] Fix region lost in /proc/self/smaps)
Date	2016-09-12 08:10 +0200
Message-ID	<sgsBj-7Yg-3@gated-at.bofh.it> (permalink)
References	<seZi1-15I-15@gated-at.bofh.it> <sfgsz-3pz-85@gated-at.bofh.it> <sfgCd-3HW-23@gated-at.bofh.it> <sfpYR-VU-19@gated-at.bofh.it> <sfwdY-4Pt-19@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw


On 09/09/2016 11:40 PM, Dan Williams wrote:
> On Fri, Sep 9, 2016 at 1:55 AM, Xiao Guangrong
> <guangrong.xiao@linux.intel.com> wrote:
> [..]
>>>
>>> Whether a persistent memory mapping requires an msync/fsync is a
>>> filesystem specific question.  This mincore proposal is separate from
>>> that.  Consider device-DAX for volatile memory or mincore() called on
>>> an anonymous memory range.  In those cases persistence and filesystem
>>> metadata are not in the picture, but it would still be useful for
>>> userspace to know "is there page cache backing this mapping?" or "what
>>> is the TLB geometry of this mapping?".
>>
>>
>> I got a question about msync/fsync which is beyond the topic of this thread
>> :)
>>
>> Whether msync/fsync can make data persistent depends on ADR feature on
>> memory
>> controller, if it exists everything works well, otherwise, we need to have
>> another
>> interface that is why 'Flush hint table' in ACPI comes in. 'Flush hint
>> table' is
>> particularly useful for nvdimm virtualization if we use normal memory to
>> emulate
>> nvdimm with data persistent characteristic (the data will be flushed to a
>> persistent storage, e.g, disk).
>>
>> Does current PMEM programming model fully supports 'Flush hint table'? Is
>> userspace allowed to use these addresses?
>
> If you publish flush hint addresses in the virtual NFIT the guest VM
> will write to them whenever a REQ_FLUSH or REQ_FUA request is sent to
> the virtual /dev/pmemX device.  Yes, seems straightforward to take a
> VM exit on those events and flush simulated pmem to persistent
> storage.
>

Thank you, Dan!

However REQ_FLUSH or REQ_FUA is handled in kernel space, okay, after following
up the discussion in this thread, i understood that currently filesystems have
not supported the case that usespace itself make data be persistent without
kernel's involvement. So that works.

Hmm, Does device-DAX support this case (make data be persistent without
msync/fsync)? I guess no, but just want to confirm it. :)

Back to linux.kernel | Previous | Next — Previous in thread | Find similar | Unroll thread

Thread

Re: DAX mapping detection (was: Re: [PATCH] Fix region lost in /proc/self/smaps) Dan Williams <dan.j.williams@intel.com> - 2016-09-09 17:50 +0200
  Re: DAX mapping detection (was: Re: [PATCH] Fix region lost in  /proc/self/smaps) Xiao Guangrong <guangrong.xiao@linux.intel.com> - 2016-09-12 08:10 +0200

csiph-web