Re: [RFC][PATCH 6/7] freelist: Lock less freelist

[Lai Jiangshan]

On Fri, Aug 28, 2020 at 12:23 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:

> +static inline void __freelist_add(struct freelist_node *node, struct freelist_head *list)
> +{
> +       /*
> +        * Since the refcount is zero, and nobody can increase it once it's
> +        * zero (except us, and we run only one copy of this method per node at
> +        * a time, i.e. the single thread case), then we know we can safely


> +
> +               /*
> +                * OK, the head must have changed on us, but we still need to decrement
> +                * the refcount we increased.
> +                */
> +               refs = atomic_fetch_add(-1, &prev->refs);
> +               if (refs == REFS_ON_FREELIST + 1)
> +                       __freelist_add(prev, list);

I'm curious whether it is correct to just set the prev->refs to zero and return
@prev? So that it can remove an unneeded "add()&get()" pair (although in
an unlikely branch) and __freelist_add() can be folded into freelist_add()
for tidier code.

Thanks
Lai.