On Thu, May 12, 2022 at 09:54:59PM +0100, Matthew Wilcox wrote: > The LWN writeup [1] on merging the MGLRU reminded me that I need to send > out a plan for removing page flags that we can do without. > > 4. I think I can also consolidate PG_slab and PG_reserved into a "single > bit" (not really, but change the encoding so that effectively they only > take a single bit). PG_reserved could be a PageType, AFAIR no reserved pages are ever mapped to userspace > That gives us 4 bits back, which should relieve the pressure on page flag > bits for a while. I have Thoughts on PG_private_2 and PG_owner_priv_1, > as well as a suspicion that not all combinations of referenced, lru, > active, workingset, reclaim and unevictable are possible, and there > might be scope for a better encoding. But I don't know that we need to > do that work; gaining back 4 bits is already a Big Deal. > > I'm slowly doing the PG_private transition as part of the folio work. > For example, eagle eyed reviewers may have spotted that there is no > folio_has_buffers(). Converted code calls folio_buffers() and checks > if it's NULL. Help from filesystem maintainers on removing the uses of > PG_error gratefully appreciated. > > [1] https://lwn.net/Articles/894859/ > -- Sincerely yours, Mike.
