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SubjectRe: [RFC PATCH V2 01/12] fs/stat: Define DAX statx attribute
On Wed, Jan 15, 2020 at 09:39:35PM -0800, Darrick J. Wong wrote:
> On Wed, Jan 15, 2020 at 02:38:21PM -0800, Ira Weiny wrote:
> > On Wed, Jan 15, 2020 at 12:10:50PM -0800, Dan Williams wrote:
> > > On Wed, Jan 15, 2020 at 11:45 AM Ira Weiny <ira.weiny@intel.com> wrote:
> > > >
> > > > On Wed, Jan 15, 2020 at 09:38:34AM -0800, Darrick J. Wong wrote:
> > > > > On Wed, Jan 15, 2020 at 12:37:15PM +0100, Jan Kara wrote:
> > > > > > On Fri 10-01-20 11:29:31, ira.weiny@intel.com wrote:
> > > > > > > From: Ira Weiny <ira.weiny@intel.com>
> > > > > > >
> >

[snip]

> >
> > Sure, but for now I think referencing mmap for details on MAP_SYNC works.
> >
> > I suspect that we may have some word smithing once I get this series in and we
> > submit a change to the statx man page itself. Can I move forward with the
> > following for this patch?
> >
> > <quote>
> > STATX_ATTR_DAX
> >
> > The file is in the DAX (cpu direct access) state. DAX state
>
> Hmm, now that I see it written out, I <cough> kind of like "DAX mode"
> better now. :/
>
> "The file is in DAX (CPU direct access) mode. DAX mode attempts..."

Sure... now you tell me... ;-)

Seriously, we could use mode here in the man page as this is less confusing to
say "DAX mode".

But I think the code should still use 'state' because mode is just too
overloaded. You were not the only one who was thrown by my use of mode and I
don't want that confusion when we look at this code 2 weeks from now...

https://www.reddit.com/r/ProgrammerHumor/comments/852og2/only_god_knows/

;-)

>
> > attempts to minimize software cache effects for both I/O and
> > memory mappings of this file. It requires a file system which
> > has been configured to support DAX.
> >
> > DAX generally assumes all accesses are via cpu load / store
> > instructions which can minimize overhead for small accesses, but
> > may adversely affect cpu utilization for large transfers.
> >
> > File I/O is done directly to/from user-space buffers and memory
> > mapped I/O may be performed with direct memory mappings that
> > bypass kernel page cache.
> >
> > While the DAX property tends to result in data being transferred
> > synchronously, it does not give the same guarantees of
> > synchronous I/O where data and the necessary metadata are
> > transferred together.
>
> (I'm frankly not sure that synchronous I/O actually guarantees that the
> metadata has hit stable storage...)

I'll let you and Dan work this one out... ;-)

Ira

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