Re: Modern uses of CONFIG_XFS_RT

Darrick J. Wong
2020-02-19T17:11:56Z

On Wed, Feb 19, 2020 at 02:38:24PM +0000, Luis Chamberlain wrote:
> On Wed, Feb 19, 2020 at 03:32:27PM +0100, Carlos Maiolino wrote:
> > On Wed, Feb 19, 2020 at 01:57:15PM +0000, Luis Chamberlain wrote:
> > > I hear some folks still use CONFIG_XFS_RT, I was curious what was the
> > > actual modern typical use case for it. I thought this was somewhat
> > > realted to DAX use but upon a quick code inspection I see direct
> > > realtionship.
> >
> > Hm, not sure if there is any other use other than it's original purpose of
> > reducing latency jitters. Also XFS_RT dates way back from the day DAX was even a
> > thing. But anyway, I don't have much experience using XFS_RT by myself, and I
> > probably raised more questions than answers to yours :P
>
> What about another question, this would certainly drive the users out of
> the corners: can we remove it upstream?

My DVR and TV still use it to record video data.

I've also been pushing the realtime volume for persistent memory devices
because you can guarantee that all the expensive pmem gets used for data
storage, that the extents will always be perfectly aligned to large page
sizes, and that fs metadata will never defeat that alignment guarantee.

(Granted now they're arguing that having a separate storage device for
metadata will inflate the BOM cost unacceptably, and wouldn't it be
cheaper if we just redesigned XFS to have 2MB blocksize, but I'm not
buying that because the next thing they'll want when pmem becomes cheap
is 1GB blocksize for Big Data applications. :P)

--D

> Luis