Re: [LSF/MM TOPIC] Future direction of DAX

[willy@bombadil.infradead.org]

On Tue, Jan 17, 2017 at 10:01:30PM -0800, Dan Williams wrote:
> >> - Jan suggested [2] that we could use the radix tree as a cache to service DAX
> >>   faults without needing to call into the filesystem.  Are there any issues
> >>   with this approach, and should we move forward with it as an optimization?
> >
> > Ahem.  I believe I proposed this at last year's LSFMM.  And I sent
> > patches to start that work.  And Dan blocked it.  So I'm not terribly
> > amused to see somebody else given credit for the idea.
> 
> I "blocked" moving the phys to virt translation out of the driver
> since that mapping lifetime is device specific.

The problem is that DAX currently assumes that there *is* a block driver,
and it might be a char device or no device at all (the two examples I
gave earlier).

> However, I think caching the file offset to physical sector/address
> result is a great idea.

OK, great.  The lifetime problem I think you care about (hotplug) can be
handled by removing all the cached entries for every file on every file
on that block device ... I know there were prototype patches for that;
did they ever get merged?
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