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

Lai Jiangshan
2020-08-28T04:04:09Z

On Fri, Aug 28, 2020 at 12:23 AM Peter Zijlstra <peterz@infradead.org> 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.