Re: [RFC] Merge PG_private_2 and PG_mappedtodisk

[Matthew Wilcox <willy@infradead.org>]

On Thu, Aug 15, 2024 at 11:41:23PM +0200, David Hildenbrand wrote:
> On 14.08.24 19:36, Matthew Wilcox wrote:
> > I believe these two flags have entirely disjoint uses and there will
> > be no confusion in amalgamating them.
> > 
> > Anonymous memory (re)uses mappedtodisk for anon_exclusive.
> > Anonymous memory does not use PG_private_2.
> 
> Also not when they are in the swapcache, right?

Correct, swapcache has no use of PG_private_2.

> > The one thing that's going to stand in the way of this is that various
> > parts of the VFS treat private_2 as a "wait for this bit to be clear",
> > due to its use in fscache (which is going away).
> > 
> > So my approach here is going to be:
> > 
> >   - Rename mappedtodisk to be PG_owner_priv_2 (add appropriate aliases)
> >   - Switch btrfs to use owner_priv_2 instead of private_2
> >   - Wait for the fscache use of private2 to finish its deprecation cycle
> >   - Remove private_2 entirely
> > 
> > Sound good?
> 
> Yes, one step into the right direction.

Cool, thanks.