Re: [PATCH 6/9] mm/z3fold: move decrement of pool->pages_nr into __release_z3fold_page()

[Vitaly Wool]

On Wed, Mar 2, 2022 at 10:12 AM David Laight <David.Laight@xxxxxxxxxx> wrote:
>
> > > Atomic operations aren't magic.
> > > Atomic operations are (at best) one slow locked bus cycle.
> > > Acquiring a lock is the same.
> > > Releasing a lock might be cheaper, but is probably a locked bus cycle.
> > >
> > > So if you use state_lock to protect pages_nr then you lose an atomic
> > > operation for the decrement and gain one (for the unlock) in the increment.
> > > That is even or maybe a slight gain.
> > > OTOH a 64bit atomic is a PITA on some 32bit systems.
> > > (In fact any atomic is a PITA on sparc32.)
> >
> > It's actually *stale_lock* and it's very misleading to use it for this.
> > I would actually like to keep atomics but I have no problem with
> > making it 32-bit for 32-bit systems. Would that work for you guys?
>
> It would be better to rename the lock.

No it would not because that lock is protecting the list of entries
that could not be immediately freed.

~Vitaly