Re: [PATCH v9 10/17] refcount: introduce __refcount_{add|inc}_not_zero_limited

Suren Baghdasaryan
2025-01-12T00:31:59Z

On Sat, Jan 11, 2025 at 3:45 PM Hillf Danton <hdanton@sina.com> wrote:
>
> On Sat, 11 Jan 2025 09:11:52 -0800 Suren Baghdasaryan <surenb@google.com>
> > I see your point. I think it's a strong argument to use atomic
> > directly instead of refcount for this locking. I'll try that and see
> > how it looks. Thanks for the feedback!
> >
> Better not before having a clear answer to why is it sane to invent
> anything like rwsem in 2025. What, the 40 bytes? Nope it is the
> fair price paid for finer locking granuality.

It's not just about the 40 bytes. It allows us to fold the separate
vma->detached flag nicely into the same refcounter, which consolidates
the vma state in one place. Later that makes it much easier to add
SLAB_TYPESAFE_BY_RCU because now we have to preserve only this
refcounter during the vma reuse.

>
> BTW Vlastimil, the cc list is cut down because I have to walk around
> the spam check on the mail agent side.
>